Danny was not a spirit of the seasons, he didn't have any idea if those kinds of spirits existed out of movies, what he did know was that for some reason the flowers were behaving rather strangely in one particular dimension right at the beginning of spring. And although he certainly didn't want to affect the place he knew he had to investigate it.
From what it seemed: strange plants that glowed just like those born in the Infinite Realms were appearing in Gotham and coming to life on their own. At first he suspected Undergrowth but the Ancient was offended by the accusation and commented that he was too busy in his haunt to care about a random city. Which turned out to be true.
Then he thought that maybe it was fine: the bright flowers seemed harmless (although they were very very...alive?) and didn't hurt anyone. That was until a red-haired girl seemed to upset them and they started attacking everyone around them; unfortunately, because they were ghost flowers they could dodge attacks very easily and the "heroes" couldn't defend themselves.
So, with no other options Danny traveled to Gotham and well, to put it simply he became a fake winter spirit; what else was he supposed to do? He needed an alibi and to spread ice as quickly as possible. Telling Gothamites that winter was coming early because of him was the least of his problems.
What he didn't expect was that after turning the city into a wasteland of ice and snow (and saving them from the invasion of ghost flowers, you're welcome), some guys in bat suits would start following him around with questions. He also didn't expect one of them to stare at him and ask if he'd be back in winter, he wondered if faking his identity was a good idea.