I don't buy it, mostly because there were no drone shots of anything like this occurring in Seville, so how does some YouTuber have the inside scoop? Call me skeptical, but I don't think it's true.
With that said, I do think Tyrion betraying, either in a small or significant way, Daenerys is possible. He strangely seems to still have some loyalty to the Lannisters proper in his sister and he constantly is at odds with Dany's methods. It could be a small gesture, like trying to sue for peace behind Dany's back with Cersei, but hey, Fredo Corleone didn't mean for his backroom dealing to hurt Michael. Didn't change the fact it did and Michael had a bullet placed in his brother's head.
So while it is possible, I think this is a guess. I also think it is more reliable than Sansa betraying Jon. For whatever reason some fans want that, but I do think the end of season 7 acknowledged that the Starks are too tight for that kind of Lannister-esque skullduggery. "The pack survives." Varys is the most obvious choice for a traitor amongst them, which would make it being Tyrion more surprising. Not saying I want this ending, or believe this "spoiler," but suddenly I could see Tyrion's fate playing out very Godfather-like. Dany doesn't want to do it, but this is "business."