Which House Was Sirius In?

[ebennet68]

No: HPFGUIDX 84568

Hello all. This is my first post and I must say how much I have 
enjoyed all of the discussion for the past few months. I have 
wondered about which house Sirius was in myself and came across a 
clue as I reread Goblet of Fire:

This is Sirius talking about Snape:
(US Edition, Chapter 27: Padfoot Returns, p. 531)
"Ever since I found out Snape was teaching here, I've wondered why 
Dumbledore hired him. Snape's always been fascinated by the Dark 
Arts, he was famous for it at school. Slimy, oily, greasy-haired 
kid, he was," Sirius added, and Harry and Ron grinned at each 
other. "Snape knew more curses when he arrived at school than half 
the kids in seventh year, and he was part of a gang of Slytherins 
who nearly all turned out to be Death Eaters."

My question is this: Why would Sirius refer to Snape as being part 
of a gang of Slytherins if Sirius was in Slytherin? Wouldn't he say 
that he was part of a gang, not specifying a house, if indeed Sirius 
was in Slytherin? This just seems like a clue to me that Sirius was 
not in Slytherin as some have posted previously. I think that he was 
in Gryffindor, as well as the rest of the Marauders.

Just a thought,
ebennet