Further proof of photoshop:
If you look at the actual wyrm, it only has "1020" as its attack stat.
Now if you say that's just because of a glitch due to how big it is...
Look at Mark's:
"33152".
So it should show at least one more digit, imo.
Finally, I'm curious as to why the wyrm's hp is 270 while all other wyrms are 280 (could be explained by using rage elixir after the fact). And why are the hps that high anyway? Theoretically, the rage elixirs and basilisk bloods should even out.
It's still possible; maybe when the attack gets so high the game does in fact glitch, and maybe he just used lots of extra basilisk bloods. AKA, we won't know.