I didn't see any news articles referencing the doctors at the hospital - but I did see articles using the Gaza Health Ministry. Perhaps that's what you mean? If so, the Gaza Health Ministry is Hamas. I stand to be corrected as I obviously haven't read all articles.
Nonetheless I don't see how doctors at the hospital would know who bombed the hospital
Yep, maybe it was the same. And maybe it wasn't. I'm don't know how doctors at a hospital would be able to determine that. I'm pretty sure it's not one of the things they're taught in medical school.
And if you're in a zone where munitions are landing all around you, and almost all of them are from a certain source, you're going to assume the next one is from the same source.
Many Hamas rockets fall in Gaza killing Palestinians. There's something like a 30% failure rate.
Yeah, that seems like a reasonable assumption, but I still wouldn't cite them on it as if they had any special insight into the source of the rocket.