Who said that the letter is specifically addressing the video of them learning together. There can be many things going on in these hotels; TV, movies, secular music, parties, etc that don't conform with the Chareidi lifestyle.

I thought the video of the learning was beautiful. The text signed by the gedolin do not mention the risk of talking to "others". There were reported issues of excessive use of alcohol, exposures to smartphones for those that usually don't use them and TV's in the rooms. I know that anonymous "askonim" said that the Gedolin were upset about the exposure to Dati Leumi, but I see no reason why we should believe this. The letter explicitly says that bochurim can go with their family. Obvious when with their family they would have epxosure and learn with Dati Leumi boys as well. This is a smear and an attempt in the media to cause more friction. Today it is hard to even believe in the authenticity of a signed letter, let alone what supposedly was the motive behind a signed letter from Rav Kanievsky שליט"א