Here's a korean web page that has a little more detail towards the end of it. Parenthesis are my on add-in comments. There's a part saying that according to Polish media, Poland was considering three other tanks which were the Challenger 2, the T-90, and the M1. The Challenger 2 was a no go because of weak success in international sales and the T-90 was no good because of geopolitics (obviously). So that left the M1 as the remaining strong competitor to the K2. A security think tank sort of group called TNI speculates that the K2 might have won because of greater willingness for ROK to export tank technology than the US, such as the 120L55 gun, armor tech, and K279 ammunition. K2 does not get produced with APS ability (even through during K2 development, APS was developed for it) but procuring the K2 tanks even without APS might be viewed as cost saving for Poland (ROK produced its own K2 tanks without APS for cost reasons too). M1 can carry 34 to 36 rounds in the turret but K2 only can carry 16 in the turret due to autoloader.
I think Poland's belief that it's air force would even get off the ground in the event of a conflict with Russia is bizarre. F-35s are an enormous waste of money. That's way off topic though. Has anyone heard any more about the potential K2 buy?
No mention of Leo 2.
Sounds like nonsense.
The T-90 would not even be considered in the first place.
The Challenger 2 in its current form is too outdated, and its modernized form has yet to be fully decided on. It is therefore a relatively high risk, long schedule program that will not offer Poland any real advantage over any other candidate.
The Abrams is American so there's that political bonus, but the switch to a diesel engine (ACE) has yet to advance from the drawing board. While demonstrators exist, there are no solid plans to add it to any existing vehicle, and when talking about its potential, I don't remember the Abrams even coming up.
Either way, it's not the only candidate. Other candidates are:
Type 10 - Japan has recently started revising its defense policy and that includes the approach toward export of weapons. They are technically not prohibited by law (domestic) from exporting to any NATO country, because the definition of countries likely to be involved in conflict is very arbitary.
Overall, Type 10 may not be the best choice but if they considered the Chally 2 and T-90, then that's not far fetched.
Leclerc - fund continued development of the Leclerc XLR under the Scorpion program, for Polish needs, and negotiate with Nexter on how to start production in Poland.
Merkava 4 - quite suitable because of its L44 gun, and would be a more direct competitor to the Abrams based on their approaches to protection and mobility.
Israel's approach to Merkava export is odd. It had offered the Mark 3 to Turkey, an unknown version to Switzerland, maybe Greece. In 2010 it showcased the Mark 4 in Eurosatory, and the Namer was a GCV contender.
However since then they were silent, and when asked about the Czech program they offered the Sabra instead.
Oplot - Ukraine has a bad reputation with its Oplot contracts, but if Poland manages to secure domestic production, that issue should be completely negated (unless they start having problems of their own, but ultimately they want to produce as much at home as possible, and Oplot is one of the least complex candidates).
Well, I'm just conveying the contents of the article and not using it as my own opinion on the matter.
About the changes to the defense matters with Japan, yes that's true. Reinterpretation of the constitution happened in 2014, new defense bills passed in 2015, and the defense laws becoming effective in 2016. Although since then, separate agreements with other countries regarding logistics sharing and tech transfers still needed to be made with individual countries. Such agreements have been made with the US, Australia, the Philippines, India, and some European countries like Italy, France, the UK and Germany. Not sure if such an agreement would need to be made with Poland first before enabling a sale of tanks. It can be further added as to what Japan has actually tried to sell abroad up until now, attempts including subs to Australia, static air defense radar to the Philippines and Thailand, US-2 to India, P-1 MPA to a few other countries like the UK and perhaps New Zealand (possible false reporting on the Japanese side), some advertising of C-2 in the ME with expressed interest but no negotiation process. I don't think there's been any effort reported about Japan trying to sell the Type 10 so far.
When you say "other candidates" do you mean other tanks that are actually part of the selection process or just "candidates" as in suitable tanks for the job in Poland?