Honestly no it's not. Lor being thankful to the Horde implies he's thankful to any help he's gotten at all, he doesn't need to say specific names when said people are part of the faction he's thanking. I used Talanji as an example, because people are freaking out over Lor'Themar doing something all characters do. Thanking the faction as a catch all for the assistance they received from individuals.
Half this thread is full of people spouting bullshit for the sake of being mad. People complain Lor'Themar is a Sylvanas shill and each time he proves differently, some of those same people suddenly cry he should be her plot slave. This isn't a lie or a blunder. A character is allowed to change or distance himself from people who no longer have his best interest. Which she has proven. multiple times. IDK, something something about this is part of his character development to stop living in her and Kael'Thas' shadow. Him thanking the Horde shows that he's distancing himself from her and considering the overall Horde as something he wants to further integrate into and associate with. After years of him being under her thumb and being accused of not caring about the faction enough (esp after MOP) it's a welcome change that he finally considers the Horde's people something to fight for and thank. Not just the BEs, not just Sylvanas, he's finally thinking on a larger less selfish scale.
That growth and distance doesn't mean he's suddenly not thankful for what Sylvanas has done. He has stated multiple times he is and this is often used against him by people who hate his character. We don't need him to restate it constantly, especially when it's never been contradicted.
Why is it a big deal that a character is distancing himself from someone who helped him, when said person starts becoming dangerous/untrustworthy? It's not. That's common sense. People are mad over nothing. Like always in these sorts of threads. Almost every damn thread I see about Lor'Themar is someone making up some insane Fanon interpretation of shit no one ever said or did, because they're mad. Lor'Themar is a Sylvanas shill, Lor'Themar is going to side with Sylvanas and betray the Horde, Lor'Themar is a hypocrite and murderer, Lor'Themar this. Lor'Themar that. You know what's all over the place? This disgusting mentality that people think is normal. I also find it funny that when the content goes live, the makers of these threads silently fuck off when people call them out on their lying bullshit.
Edit: Also saving his people doesn't only include one event. The salvation of the BEs is due to Sylvanas, the political ties granted by being associated with the Horde, the soldiers sent mentioned earlier, Velen and a masochistic Naaru, the dragons for hiding away and protecting their Sunwell Energies as a girl, and even fucking Illidan. Sylvanas alone isn't the reason why they're still alive or recovered, she was just one major part of a process. Forgive a dude for saying 'Horde' to cover all those times. Maybe he should've said 'Horde, some Alliance peeps, an edgelord, and some dragons' if we're going to cry over specifics.