Cohan doesn’t even do a simple check to see whether trades of this size are unusual, on a normal day. (Spoiler: They’re not.)
In order to provide evidence of insider trading, you need two key ingredients. You need to show that someone made a profit and you need to show that they had inside information. In this case, Cohan provides neither. He’s basically p-hacking: He’s saying that if the people doing these trades had been insider trading, then they would have been insider trading. Which doesn’t really get us very far.
Cohan also tends to ignore the more obvious explanations for what is going on. The biggest trade he talks about took place “in the last 30 minutes of trading on June 28”—which also happens to be the very end of the second quarter. Big trades always happen at the very end of the quarter; it would be more surprising if there wasn’t a big trade around then.