I am pretty sure this is an e46 generation which was offered with a 3.2 inline 6. They did offer a v8 for this generation but only on the gtr which I dont believe this is. Also the v8 offered on that gtr was not only not a quad turbo it was not a turbo at all.

BMW did actually make a quad turbo but it was on an inline 6 and not a v8 and wasnt that great in terms of additional power because they were sequential and nested or something like that.

So unless this guy completely swapped his bmw engine for an engine from another manufacturer, which seems very stupid if and expensive after buying an m3 (if this is even an m3) he is just lying and being pretty stupid about lying too.