You are both in Vibranium III
Your opponent must really suck or just hasn't played much BGs yet this season.
don't worry they have the baby bgs coming out with season 34 you can have fun there
Battleground isn't fair. It's not designed to be fair. You fight whoever is in your tier at the time you press match. Hope this helps.
That's the problem when everyone is thrown back to diamond 5 at the start of the season and fat accounts don't actively push towards GC, taking their own sweet time to move towards GC
You will meet such accounts many times as many players are not in a rush to get to GC for 10k radiance which can't buy you much in store