Hrm, strange. Tried on iOS and didn't encounter that. However, the fact it's trying to download "watch" (which is the path of the page in the URL) leads me to

Hrm, strange. Tried on iOS and didn't encounter that. However, the fact it's trying to download "watch" (which is the path of the page in the URL) leads me to suspect there was a server issue that caused it to return the page as a file instead of actually serving it as a normal HTML page. /shrug