I don't even think the SEC would have to characterize the WSB commenters as a group, merely that "alone or with 1 or more persons" they caused trades that increased GME's price and that their goal was to cause others to buy/sell the stock. The real question is why wouldn't the SEC get involved!
15 U.S. Code § 78(i)(a)(2) - Manipulation of security prices
[It shall be unlawful...] ...to effect, alone or with 1 or more other persons, a series of transactions in any security registered on a national securities exchange, any security not so registered, or in connection with any security-based swap or security-based swap agreement with respect to such security creating actual or apparent active trading in such security, or raising or depressing the price of such security, for the purpose of inducing the purchase or sale of such security by others.