The de rosa most people think of, and the one you mean, is Ugo de rosa (and family) of Milan. There was also a builder named de rosa from Naples, and this is that de rosa. It is likely a de rosa, but not the de rosa you were thinking of.

I've come across them before - they seemed ok. Never ridden one. They're a little crude compared to Ugo de rosa.

For what it's worth, I would consider it some what deceptive to sell this as a de rosa without the explanation/disclaimer. It is, technically, a de rosa...but if I were selling one, I'd have called it a Naples de rosa to avoid confusion.