> Pretty sure it would downclock if i removed it. So it works without a fan, but not without a heatsink

The Raspberry Pi 4 will throttle performance at 80C (if I recall correctly) but it can work without a heatsink. I have a R.Pi 4 working without a passive cooler in an enclosure and it reports 55C-62C most of the time.

> I bet the keyboards have a heatsink for the Pis built in

You are right, both models use a heatsink. The PCB is also different, although the respective CPUs are standard Pi 4 or Pi 5.

Incidentally, the CPU in the R.Pi 400 has a higher clock rate than the standard R.Pi 4, so it performs better.