Who phoned you? Celebrity in Australia? You certainly wouldn't want to cruise with them in the future. I wouldn't! Has anyone ever been denied boarding because of booking in the US? I certainly haven't heard of such a case. I'm sorry this advice caused you stress at the time. Think about it. This advice wasn't for your benefit. I have booked all my overseas travel, in all forms, direct overseas, using my Australian address, without any problems. I'm pleased you had no problems and had the most fantastic cruise.
Since the pandemic, I'm happy to be cruising in Australia, booking my cruises in Australia.