"Custom CPU" seems like a bit of a stretch. They have ASIC people on staff (eg https://rocketreach.co/ya-chau-yang-email_61973123), but based on the fact that you can flash basically all their devices with OpenWRT (including those disc-shaped APs), I think the "ASIC" is just a conventional ARM or MIPS core with some peripherals geared toward hardware acceleration of common network tasks— switch routing, vlan tagging, etc.
This page talks about the specific features available for hardware offloading:
This page talks about the specific features available for hardware offloading:
https://help.ubnt.com/hc/en-us/articles/115006567467-EdgeRou...