lol this is not a dumb question. This is a good question, and one that applies to every religion and historical event.
It’s up to you if you believe what happened or not. I’m not going to convince you.
But what I would say is that you should not concentrate on the miracles. They mean nothing. Sikhi doesn’t care for miracles in the slightest. What you should concentrate on is the message, the teaching.
Maharaj condemned miracles performed for personal glory… The greatest miracle is not to perform a miracle, in spite of having the capacity to do so.
Care not for the amount of time Maharaj spent in the river, care more for the message he had when he came out. The Mool Mantar. Look into that.