Which one is right in terms of tense aspect a) what happens, or b) what happened?
A bus suddenly braked, and all the passengers lurched forward from their seats. A middle-aged man shouted, 'What happened(has happened, happens), what happened?' The bus driver, wiping off his forehead, turned around and said, ' A reckless driver just cut me in. That what happened."
A reckless driver cut me off (not in). That's what happened.
The event was fast and finite and now in the past.
This may be one of those times when my British cousins may use present perfect.
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.