Just from looking at pictures, I can tell you the difference is in his PDef, MDef, Crit and to a much lesser extent Block.
"Your battle rating is determined by adding all of your battle stats together, but with Magical Attack multiplied by 1.05 (and rounded down), and HP divided by 5 (and rounded down)"
From what I can tell from playing around with astral this seems to be true, 1 point in all stats but HP is 1 point in BR and 1080 hp came out to 218 BR
I just find it odd, I mean to BR the person with the higher BR should win, but I win easy
edit: Psure its a bug, I used some pots and went up to 9.6k. The pots wore off but my BR didn't go back down.
BR after using pots that wore off:
BR after using another pot AFTER THAT: