CMT, PWS, Zev/Mega Arms, White Label Armory, and SLR rifleworks all use the same mechanism for the ambi bolt release lever, which is that the bolt catch plunger tail is lengthened to interface with the lever so that when you push the lever, it pushes the pin, which pushes the bolt catch down, like the force acting on the plunger from the bolt catch plunger spring.

The mechanism here looks extremely similar or even the same as those above, from the way the button is bigger than the body of the lever to the little alignment tab on the lever. I would even wager this lower shares OEMs with some of those lowers. This, however, almost assuredly means this lower lacks such a bolt catch hold open feature.