Jensen had a different kind of ban than you do. His ban was the type of ban that Tyler1 currently has. All of his accounts were banned and any new accounts Riot could tie to him would also be banned. He was also indefinitely banned from competitive play. When Riot unbanned him, they allowed him to create new accounts without instantly banning them, as well as eventually allowing him back into competitive play. However, he did NOT receive ANY of his banned accounts back.
As for you not getting a warning, did you receive any punishments prior to this? If you did, then those punishments served as a warnign that your behavior was unacceptable. If you didn't, then Riot likely believed that your behavior was severe enough to escalate straight to a permanent ban. In some cases of extreme toxicity Riot will escalate an account straight to a permanent ban. These cases generally include (but are not limited to) things like racism, sexism, homophobia, death threats, etc.