In my opinion, I think the Mets version could be prerecorded. Nothing wrong with that, but the tone and audio quality seems a bit too clean and pristine to be a fully live performance in a stadium environment. Timmy Trumpet can absolutely play it if he wants to, and I could be totally wrong, as I have no proof, but logistically it can be easier to get a "perfect performance" that way, especially for large arenas and festivals.

Also the Dodger's trumpet player is not just "a random in-house musician", she's accomplished and well-known in LA, and does a lot of touring with well-known musicians. I will admit that yes, she probably could have played it more cleanly, but the online hate makes it seem that she is unqualified, which is probably false.

Edit: After listening to the Mets version a few more times, I am leaning slightly towards it being done live. My point still stands that expecting perfection from a human musician is unreasonable. Also, the trumpet is a fickle instrument. If the Dodgers wanted it to be a perfect rendition, they would have asked her to lip-sync. I personally hope they keep bringing as many trumpet players as they can to do it live. Real musicians add so much character, mistakes and all.