What could be growing?

Last week I was at my LHBS and they gave me a pack of Wyeast Lambic blend for free, because it was 10-11 months old. I smacked it and set it aside to see what might happen.
A week later, it's starting to swell.

I wonder if the yeast is dead, and that's the bugs, or if the yeast has survived.

Is there a way to figure out what's growing when I cut it open?

I'd bet both the yeast and bugs are working. The bugs usually take a long time (months) to really sour a beer so I'm betting the yeast are swelling your pack.

Edit: well the bugs can sour sooner depending on what they are. I'd still say just brew with it and see.

You can probably tell the difference if you took out a sample and plated it to see the different colonies, but it might be hard to tell between them. Not worth the effort in my opinoin.