I didn't notice him wallhacking. Getting headshots with a sniper rifle is kinda luckbased for me, and for everyone i see. People are moving, the scope comes in slow, theres active sway scope up or not, if he can aim for 4 hs in a row and get them i cant imagine how ricockulous he is when just trying to get kills. My bet, just like it always is with everyone else I see, the headshots were a matter of luck and circumstance, not botting or skill.
Greg did not consult anyone else before this ban, as far as I know. This tells me he was pretty sure about it. Although we have our differences, when he's that sure, I would lean towards trusting him.