The Gathering was filmed 4:3. It was the only one filmed that way. The DVD definitely has that. When it aired on the sci-fi channel they cropped it to make it look like it was wide-screen so it would match the other episodes, so perhaps this video is using the same source they did.
"The Gathering" was filmed the same way as the rest of the series, in 1.65:1 first and the cropped to 1.33:1. TG is only released in 4:3 because Warner's already spent money redoing the episode for the Special Edition (and as far as I know iTunes had the original 1993 version available in the US years ago, but the DVD's have received the 1998? Special Edition, along with the other download services).
So, maybe the Sci-Fi channel is cropping it on their own; unless Warner actually created a HD widescreen version that was just for broadcast.