If evasive maneuvers were required, I think that would reasonably get into 91.13 territory. I'll bet the FSDO could make some hay out that if they really wanted to.

It would be unreasonable to insert yourself into opposite-direction traffic without any attempt to coordinate in advance. I would think that traffic already in a pattern (especially the correct pattern for that RWY) and making radio calls would have at least a "common law" right of way.

If you have the N-number, let the FSDO know...if nothing else they can talk to the dude and maybe set straight. Or he may already be "known" to the FSDO, something like this could be a data point that informs how they they handle his next actual violation.