That makes sense. I had looked at rhe wiki before posting, but are boosters on shorty AKs the same thing?
Kind of. The big multipart muzzle devices on the shorty bulgarian AKs or the famous one from the AKS-74U are basically little gas chambers at the muzzle to dam up gas to create more pressure to cycle the action, because these short barrels do not leave enough time to build up enough pressure. The bullet uncorks the bottle too early if you will.
I think they're more / just a conical type of flash hider.
A case of it depends. Though most of the time AK muzzle devices are compensators and/or brakes and not flash hiders. The famous slant cut muzzle device does nothing to hide the flash and the AK-74 one is a flash enhancer if anything, but a very effective brake and compensator. Off the top of my head I cannot think of a military issue AK coming with a flash hider except the Galil and R4 and related rifles.