BU/BB situation - BU cbets 2/3 (60size if precize) and when turn is 5c

IP player just betting K5/Q5/A5 for ''no reason'' obv there are reasons but I'm not sure which one and when it can be used

and OOP responce

I've looked through all rivers, any river is check down except 8, but I'm not sure it is even important. As OOP donking that river bunch too

only reason that make sence is mergy bet - some worse calls and many better folds(blocking 2 pairs). Kinda ''non natural bluff that can showdown and win''. But actually if we dont bet turn we still going to showdown enough and win vs Ahigh FDs and 54 type of stuff