How do you know the comment was actually from Musk? My guess is that some crank on the internet sent Edge an email claiming to be from Musk, and they published it without doing an identity check. Then the real Musk found out and asked for it to be taken down. The sentence "10 years at most" seems especially stupidly overconfident and inarticulate (and thus unlike something Musk would write).
Just a quick update of a sort, according to this article, the comment was genuine, and that he will write something longer on the topic.
Elon Musk submitted a comment to edge.org a day or so ago, on this article. It was later removed.
Now Elon has been making noises about AI safety lately in general, including for example mentioning Bostrom's Superintelligence on twitter. But this is the first time that I know of that he's come up with his own predictions of the timeframes involved, and I think his are rather quite soon compared to most.
We can compare this to MIRI's post in May this year, When Will AI Be Created, which illustrates that it seems reasonable to think of AI as being further away, but also that there is a lot of uncertainty on the issue.
Of course, "something seriously dangerous" might not refer to full blown superintelligent uFAI - there's plenty of space for disasters of magnitude in between the range of the 2010 flash crash and clippy turning the universe into paperclips to occur.
In any case, it's true that Musk has more "direct exposure" to those on the frontier of AGI research than your average person, and it's also true that he has an audience, so I think there is some interest to be found in his comments here.