He's the mayor regardless of your feelings on the matter, and the Nicks are the sportsball team for the city he's mayor of. This isn't partisan thing just because he exists and is doing what mayors do. If he tried to gatekeep something for only his party, or ideology then it'd be partisan. But he didn't because it's a NY thing, not a partisan thing. See the difference?

how is that partisan politics? showing up as a mascot for a random human interest story is the primary function of a mayor.

You are projecting your political feelings. He’s a popular mayor who loves the team.

This is very standard and innocuous. This instance only stands to you because it makes you uncomfortable. Own up to the specific reason for that instead of acting like the existence of "politics" in a general sense is somehow evil.