If the video content is loaded from the same place as the ads, and the blockers are blocking the source, that statement would make sense. I'm not sure it's gaslighting. Passive aggressive? Maybe but the point is to tell you not to do this so perhaps that's justified?
"Buffering issues" implies the video would take longer to load, or have to pause during playback to load more of the video. Blocking the servers providing the video content would mainly result in a complete inability to play the video.