Did he really say that specifically about the "current trend of deep learning using neural networks"? Surely he would have been speaking more generally about AI?
See the references I give below; if he is talking about general trends in AI and is giving an estimate of 7 or 8 years for emergence of AGI, where is he basing it on? Is he basing the estimate on unseen breakthroughs (i.e. unknown unknowns) to occur within that 7 or 8 years frame, or is he talking about current DL techniques pushed to their limits? For the former, nobody can make a reasonable estimate (nature of unknown unknowns) and for the latter, most experts in the field seem to agree that that current techniques do not lead to AGI. (Like have you seen how hard it is do things like visual question answering (VQA) or text summarization tasks? These are much much simpler than AGI but like AGI do not lend themselves easily to supervised learning.)
He talks about AI in those links, and does not mention specific approaches like DL etc. He's been around long enough to see the different approaches to AI, so as to not confuse it with a specific technology. I doubt it would even occur to him think AI=DL.
Many people have made estimates for human level AI, without relying on specific technologies. e.g. Vernor Vinge, Ray Kurzweil, Bill Joy. For example, the lower part of Vinge's range included the 2020's - for his prediction made a few decades ago.
Is Musk accurate? How can any of these be very accuracte, with so much unknown, as you note. Is he optimistic (er, predicting too early)? I guess so.
I'll note that even for Musk's own companies, upon which he is the expert, and upon which he wields more influence than anyone, he is notably optimisitic in his estimates...
Anyway, the answer to my question is: no, he didn't speak of those specific technologies, just AI.
