Almost the same but I think there's a nuance in emphasis: אתה היית שם, אני לא (הייתי שם). The way it is written here it implies: it's you who were there, it wasn't me (so why are you asking me what happened or something like that).
"you was there not me" why not "was"? some unexpected changes in english? here it is singular you...
you can never say "you was" - that is incorrect English. It's "you were", both when you talk about one or more persons.