So the alert was added along with BIP9 (version bits) and is triggered when:

> If at any stage 50 of the last 100 blocks have unexpected bits set, you get Warning: Unknown block versions being mined! It’s possible unknown rules are in effect.

It's likely  :)the node is running either BU or bitcoin Classic and that is what triggered it. In an attempt to stay apolitical, if you support that you should stay there, if you don't, find a SegWit signaling node, if you don't care find a node that signals that (thanks to veqtrus's graph we now know that's ~90% of the P2Pool network).

Right now the node is mining valid shares and will continue to until a soft/hard fork occurs, at which point Forrest will likely release a hard fork of P2Pool.... after that it gets very political and messy so I'll stop there