It turns out for that IVs are doubled for the metal generation (because IVs go up to 31 in the new games).
So it would go like this:
Hitmonlee attack, base = 120
At level 100 max according to POTDC = 338
[ (IV * 2) + (2*base) + (EV/4) ] * (level/100) + 5
or
[ (15 * 2) + (2 * 120) + (255/4) ] * (100/100) + 5
or
30 + 240 + 63 + 5 = 338
So it's that that was throwing me off. It also explains why his max attack is 339 according to: pokemon.marriland.com/statcalc.php
Because 31 is one more than 15*2.