The phrase “Did he died?” is a running joke in the comment sections of YouTube and similar websites. People use it when something mildly dangerous happens in a video (e.g. when someone trips over) because it is, presumably, funny.
The fact is, “Did he died?” is perhaps the most overused “joke” on the Internet, and although it may have been funny the first few times someone used it, I find it hard to understand why people still continue using it (Google alone returns about 10 million results for “did he died” as of March 2015). What I find worrying is that non-native speakers could easily pick it up and use it even in normal conversation, unaware that it is a joke (English learners often struggle to avoid the past tense after “did”).
The origin of the phrase is unclear, but it probably started as a genuine error. Nevertheless, it is pointless to point out its ungrammaticality to the people who use it, since the error is usually intended. If you see someone using the phrase, you can simply ignore them; the only grammatically correct form is “did he die”: