Stop pretending Teemo was buffed, he was nerfed.
Halving the timer from 10 minutes to 5 minutes ruined Teemo's strongest asset, his map control. Additionally, his passive was most abusable early game. Now it's weaker early and stronger later, but overall I think his level 1-3 ambushing was the only thing keeping him from being absolute food for other top laners. His bomb arm time was also increased from 1 to 1.5 seconds, making it even easier to avoid the shrooms when you see him place it.
Being able to chunk a mushroom into a fight is nice, but you can only refresh the damage, it doesn't stack. His real power was unsuspecting enemies walking onto a bomb and being chunked for 30% health. Now that's half as likely since his shrooms last half as long as they used to.
tl;dr Teemo's strongest attribute was heavily nerfed and they're calling it a buff.