According to this, no, the percentage of HP remaining is used to determine a victory; if the players have the same percentage of HP remaining, THEN total HP is used to determine a winner.
We had 1 mon each, so 1) is a tie; moves on to 2).
I had 100% HP remaining, he had 75% (took Leech Seed + Poison damage at 100% HP = 1/8 damage each, so 24-25% max HP chopped off).
So, according to 2) a, I had a higher average HP percentage, so I won. Step 3 would only happen if we both had an equal percentage.
Either PGL has its order of operations in the wrong order, or 100 > 75 = false. So, one of these is wrong and I'm losing points to it.
edit:
source sorry