Fermentation appears to have restarted in my Barrel

Okay...I'm afraid I know the answer to this but...

I have 5g of Imperial Stout in an Oak Barrel that was part of a 15g batch. It went into the barrel Sept 18th...so basically almost 3 months ago. I opened the barrel 2 weeks ago to check it...didn't put anything into it and used sanitizer before removing the bung and when putting it back. The bung was off for maybe 30 seconds. No Krausen and the the beer had evaporated perhaps half-an-inch. Tonight the bung came flying out of the bung hole (cornholio!) and there is a thick krausen on the top. I tasted the beer with a well sanitized wine thief...it's delicious and I'd love to bottle it up this weekend. I put the bung back on and it came flying back out shortly after. We have been keeping the house slightly warmer...perhaps 2-3 degrees in the last few weeks.

Do you think we have an infection or do you think the warmer house temps restarted the yeast? As I said, the beer tastes fine...but the airlock I just put on is going crazy!

Whats the gravity? It's probably fine but of course you shouldn't bottle it until fermentation is complete, what are the specifics of the barrel?

I haven't taken a new gravity reading...but it was a bit under attenuated when it went into the barrel...1.022. The barrel is a Bourbon Barrel (20L) that I had Potassium Metabisulfate in and then about a 5th of bourbon for a week that I rolled around every few day before putting the beer in.

The activity seems to have mostly stopped now.

I should probably take a gravity reading.