Possible Tahm Kench jungle bug

Today in a Summoners rift normal 5v5 on patch 5.18, on my team was a Tahm Kench jungle, at first I thought it was quite odd. Then to add to that he built devourer, at this stage I thought it was very weird. He gets sated on a stalker's blade, he then sold it built some tank items and got cinderhulk. That made most the team happy cause he finally went tank. But then some friends and I noticed he still had the Sated devourer buff. He was getting the extra benefits and still was going tanky with the sated effects. This obviously was incredibly strong as he had 4 thousand health with the Sated devourer effect. Note it was just the effect it was also dealing damage. They ended up surrendering a game that they possibly could of won if our Tahm didnt do this. Im unaware of how he did it step by step seeing I tested it on Xin Zhao in a custom game and once i sold the sated devourer item and bought cinderhulk the buff didn't carry over.

First time posting on here hope this is enough.