Less likely, there's a simpler explanation. Cooler air is more dense than warmer air so once thawed the air fills more of the bag. So depending on how much air got in at first it could fill the bag significantly.

Bacteria that causes botulism like very moist conditions, it's associated more with canned foods than dry goods. It's not impossible! But its unlikely.

You know what else produces gas? Bacterial reproduction. That’s EXACTLY why jars have that pop up seal and there’s warnings not to use the product if it’s popped.

So does botulism and other bacteria feeding. If a ferment was not intentional, it's best to err on the side of caution and not eat it. Since this isn't typical behavior of a packet of Sriracha at Starbucks and most hot sauces with some sweetness are boiled to stop the ferment, it would be insane to assume any of these packets are safe.