You are correct, I am sorry. In Pennsylvania, there must be a unity of interest in joint tenancy. That's not universal (for example Connecticut allows otherwise).
I didn't argue one house was a business, it was just a warning that if they were engaging in such a business that this would be income rather than capital gains (yes provided it's not held for longer as an investment/rental use). However, most people use "flipping" for shorter term than that.

