So my boss and I had our yearly performance review and one of my comments was increased workload (due to us being a person down due to paternity), poor planning, a constantly moving target (sound familiar?) and friction when raising concerns.

My boss' comment surprisingly acknowledged all of this, and he did admit to "having his head bitten off by me on more than one occasion".

And he also said that I severely underrated myself in the review (we're supposed to put ratings on our own performance and the boss is supposed to do the same) -- with him putting my rating higher than my own.

Personally, I'd rather it be this way around. Ranking yourself higher than your boss's ranking of you would likely be seen as arrogant here. Or that your boss is an asshole.