Oh man, that really sucks, I wonder how it exploded

The partner in crime thinks that the chemicals become unstable if you don't use them for a long while. Add in a year of fluctuating cool temperatures (as this is in a basement setting) and I guess they become The Blob.
Now I'm just trying to figure out how to clean it all up, as it's only one of the two part mix that oozed everywhere.

Yeah, certain mold mixes have a short shelf life. You need to use most within a year or they get weird.