Although I am sure there are much more informed opinions than mine in here, I believe that pro status has more to do with being paid for the fight itself. A lot of amateurs receive free equipment in a lot of sports. Some can even be paid by their sponsors while retaining that amateur status.
In some events, you can receive prize money (if you win) and still retain amateur status. The big difference is if you are being paid to show up and fight (even if you lose). This makes you a professional fighter as opposed to an amateur competing for prize money.
Note: Different sports, different orgs, and different states can all have different rules here so please don't take my post as gospel.