No one’s criticizing you. They’re educating you. You’re far from the first person that’s come through here who thinks the oil light means “stop when convenient.” The oil light means stop right NOW. Unfortunately, you’ve learned that the hard way and will have to replace the engine.
I will criticize one thing, however. . If the dealer really told you that maybe the oil light was on because your gas cap was off, whoever told you that is a clueless idiot who has no business working anywhere even slightly related to the automotive industry, and you should never ask that person anything ever again.