That isn't the whole story according to the book. In the book, he explains that he tried posting hundreds of messages under his own name, but there was some mysterious limit on multiple posts, so he created the extra accounts. Michael Lewis wrote that he didn't try to make them look like separate people, just separate accounts. Furthermore, he posted the exact same message, either through lack of guile or lack of intent to deceive.
In his emails he said he liked the stock and owned it. How is this deceit? He liked it and owned it. He said the price would go to such-and-such. It did. If I post here on HN as raganwald and again as regbraithwaite, is it deceit? How? There is no strong injunction against multiple accounts on HN.
Given that the internet does allow you to create multiple email addresses and that Yahoo doesn't actually insist on one account per real person (unlike, say Facebook), Michael wrote that it is far from clear that he was breaking the law, which is why the SEC settled: They were desperately afraid of losing the case and having the emperor revealed to have no clothes:
There really isn't anything different between Jonathan Lebed and a brokerage leading an issue, except membership in a cozy little club. It's total clutching at straws to say he pumped and dumped but companied are allowed to hire PR firms to talk up their prospects.
Sure, the SEC will always try to find some trivial technical difference to justify closing the Jonathans down, it's just like a casino kicking a card counter out for "cheating."