I don't know what's going on here but it looks very much as if someone tried to disguise a lethal crack with automotive epoxy (Jiffy Weld?). Were this a proper MIG or stick weld you'd see evidence of grinding in order to smooth out the weld and I don't see any sign of that.
Run a file over the joint to see how soft it is compared to the surrounding metal.
You may have learned a $7 lesson!
The material doesn't appear to be overly soft when I ran my file over it a few minutes ago. But you're right about there not being many grind marks.