They didn't mention closed bolt operation, but I suppose we can be sure about it?
... I can think of only two assault rifles that were open bolt, and only one of those was even quasi mass-produced. Of course it's closed bolt.
A safety lever is more simple to the gun designer, but I was thinking KISS for the logistics soldier who's super-stressed in an ambush.
Would be too bad if he musters the courage to expose himself for
saimed shots after 10 seconds and then can't shoot because the lever is still on safe.
Why do you think it takes ten seconds to aim a rifle shot, and how long do you think it takes to sweep the safety off even if the soldier realizes that he's derped up and somehow forgotten to take it off safe?
Alternative safety systems have been tried for assault rifles, namely double-action triggers like in handguns. Beretta considered the concept early in the development of the ARX-160 and dropped it quickly. They're a bad idea.
Handguns live in holsters, and a holster that's designed by anyone who doesn't have a hole in their head will completely enclose and protect the trigger. The danger of negligent discharge of the weapon comes from the user accidentally fingering the trigger when they didn't intend to, which does occasionally happen.
Rifles don't live in holsters. Rifles live on slings most of the time, and held in the soldier's hands at a low ready much of the time. Branches, bits of clothing, and other environmental hazards will conspire to snag the trigger, so just a grip safety isn't adequate at all. It's not an issue of designer convenience; grip safeties are extremely simple and no more complex than a manual safety. The issue is that the rifle absolutely needs some means of positively locking the trigger out because that trigger is exposed.