As far as I know, only the sock has to match the rest of the diemensinons are always the same size (area CPU, thickness etc.).
But there are two things to keep in mind:

- The height of the fan must fit into the case.
- The RAM should have enough space on the side.

Why it says mechanically incompatible is a mystery to me, and the website doesn't say anything more about it.

hmm but the MB has the socket LGA 1151 and the cooler supports this socket...

This probably means that the cooler would have enough capacity to cool the CPU even with the enormous heat generated by massive overclocking, but you cannot mount this cooler mechanically on this socket. An adapter or similar would probably be necessary.