It is hard to say, I am not involved in ether project. CARP was definitely created in response to perceived deficiencies(both technical and political) in VRRP. I agree it does sound like picked the same number out of not a little spite. However the openbsd project has this to say about picking the ipnumber.
"As a final note of course, when we petitioned IANA, the IETF body regulating "official" internet protocol numbers, to give us numbers for CARP and pfsync our request was denied. Apparently we had failed to go through an official standards organization. Consequently we were forced to choose a protocol number which would not conflict with anything else of value, and decided to place CARP at IP protocol 112. We also placed pfsync at an open and unused number. We informed IANA of these decisions, but they declined to reply."
Obviously the correct thing to do is get numbers via IANA but what is the least wrong thing to do when your project is too small to do this. Camp on unused numbers? If your project is successful enough they will eventually be granted. Use whatever number matches the closest fit? Pick some screwball assignment that failed to gain any actual use?
"As a final note of course, when we petitioned IANA, the IETF body regulating "official" internet protocol numbers, to give us numbers for CARP and pfsync our request was denied. Apparently we had failed to go through an official standards organization. Consequently we were forced to choose a protocol number which would not conflict with anything else of value, and decided to place CARP at IP protocol 112. We also placed pfsync at an open and unused number. We informed IANA of these decisions, but they declined to reply."
https://www.openbsd.org/lyrics.html#35
Obviously the correct thing to do is get numbers via IANA but what is the least wrong thing to do when your project is too small to do this. Camp on unused numbers? If your project is successful enough they will eventually be granted. Use whatever number matches the closest fit? Pick some screwball assignment that failed to gain any actual use?