Read the entire announcement. If it does not explicitly state that skating up is allowed, then no, a pre-bronze skater cannot enter bronze. The rules in the USFS Rulebook are written for qualifying competitions; clubs can adapt them, with permission, for the non-quals, so the announcement is the gospel there.
That said, in smaller open competitions, it's not unusual for events to be combined when numbers are low. You can put a note on your entry (or e-mail the registration person) saying that you are willing to skate up if they want to combine the group.
This is something you want to check yourself though. Taking the coach's word that it's okay might not be the best way, as not all coaches are 100% up on Adult competition rules. Verify it yourself and save the e-mail and the name of the person you clear it with.