I didn't interpret it as an accusation. I interpreted it as he wrote: a suspicion that something other than RT's algorithms is a non trivial contributor to their success. He gave an example of insider trading, but it could be something else ranging from the equally sinister lying about outcomes (e.g. by creative accounting of what counts as a return) to the less sinister better access or timing to information anybody else has that makes the algorithms more effective and far less relevant, and many other things.

His other point about the rarity of regularly beating the market certainly supports some amount of skepticism of RT, in my view. It's extraordinary, and it's an extraordinary claim that suddenly the particular talent at computational trading at RT is better than the legion of super genius other quants and techies who have been doing this for years.

Disclaimer: I haven't a dog in the fight with respect to supporting or taking RT down. As I see it, being a small time player, my trading strategies are necessarily constrained to the point where RT's methods, legit or not, aren't applicable. So whether they win or lose doesn't make a difference to me.