A pump and dump would require the same entity to be doing the buying, pumping up, and then dumping the asset.
The SEC didn’t buy, nor did it sell, nor did it pump up the price (someone pretending to be the SEC pumped up the price).
Even assuming that the “largest pump and dump” claim is correct, at most, the SEC was used for that purpose and isn’t “responsible” for it.
Which may or may not be true, if they were using "password123" then sure that's negligent and they'd bear some of the responsibility, but it might not have been the SEC's fault at all.
It seems like SEC didn't even have some basic protections in place for their Twitter account, like having 2nd-factor enabled. That feels kind of negligent already, even if they had a very secure password.
How do we know it's not an inside job? Pretty tempting to pull a twitter account takeover and make potentially millions if you a lonely cog in the SEC wheel.