I don't think I've ever heard this sentence with the definite article before the דבר, it usually sounds like זה לא אותו דבר. Is it just me mishearing, or do the locals actually often make this mistake? Or is it not a mistake at all, but depends on context?
Locals user both interchangeably. Your hearing is excellent for a foreign language.
there is דָּבָר (da-var) meaning something; דַבְּר (da-ber) meaning speak (order someone to talk); דֶּבֶר (de-ver) meaning plague disease; and דוור (da-var) meaning mail carrier.
You are right, but that does not answer his question. There is no את because "the same thing" is not a direct object here.
I think some weird thing happened that didn't let the word "thing" appear when I was practicing. I was looking for it but didn't find it.