Because McGonagall is mad for Gryffindor and merrily broke the rules that first years can’t own a broom because Harry was a baller flyer and Gryffindor desperately needed a good seeker and some Ws.

I hate that I read each book once, only saw like two movies, and the details just sit in my mind forevermore.

I think the only one that makes sense is if they used his money or put it on his tab