First off all the title is clickbait, Sonnen didn't even say that. He said Penn would come out on one side of the bracket and Khabib would come out on the other side of the bracket for the GOAT LW.
Second, yes Penn probably could beat him, a prime Penn. Whoever said he couldn't...yeah he's been washed up and yes overall the talent pool and skill has increased since Penn's prime era, but Penn was the LW Goat, still is really...and his tools translate stylistically to beat Khabib potentially.
Penn did lose to GSP but it was a competitive fight too relatively, that was a prime Penn. So it's easy to see how he could remain competitive or beat Khabib at 155.
Third, everyone needs to stop dick riding recency bias so hard. Who has Khabib even fucking beat? Let's be real here. Everyone bashes McGregor for no title defenses but who has Khabib beat? He beat Al Iaquinta, a journeyman, for the title and then he beat McGregor (easily his best win) and Porier - who's not some amazing name in reality. He beat a FW for a vacant title.
Khabib is undefeated and he's a great fighter, but let's not go full Joe Rogan and crown him as the GOAT of his division like Rousey and Holloway were without fully deserving it.
Khabib needs to defend his belt and beat at least 2-3 more legit - elite opponents before we can talk about him being such an amazing figure. Really, let's slow it down. His 2nd and 3rd best wins ever are against Dustin Porier and RDA prior to a title run/steroid cycle. He should have a loss to Tibau on his record.