Rust or Not?

As others have said, it’s rust given where the bubbling is located and you don’t know for sure if it was bare metal before it was painted.

If it’s there, it’s also on the inner wheel well. Odds are really good it will also appear on the passenger side soon too and lower rear quarter panels. Only way to get rid of it is to strip it down to metal and then cut out the rust and weld in new metal.