You are both right and wrong here. I'll talk you down.
So, here's the thing. Yes, you are completely right, there will be a doubling of battery technology in the next ten years, and a 40% (or something) increase by the time the gigafactory opens. This is most assuredly going to happen. This is why Tesla keeps saying they'll have a 30% cost reduction, and why Elon even says he thinks they can probably do better. I think they will. I think 30% is a conservative estimate.
However, this isn't actually big news. For the last 30 years or more, battery technology has been improving at between 5-14% per year (depends on who you ask, I usually quote 7-10%). Tesla has known this since the start, and has said it on many occasions, and rested their entire business plan on it. That's the point of going expensive car -> less expensive car -> even less expensive car. Because they knew battery tech would get better and cheaper, steadily, over time.
So this isn't any sort of secret signal, it's just an acknowledgement of trends which Tesla has acknowledged many times before. Now, it certainly can be true that we, as investors, can understand this before the rest of wall street does, or while wall street is skeptical and thinks that Tesla's claims are coming out of nowhere because they don't understand technology. But this isn't a special hint of some secret plan Tesla has, it's just JB reminding everyone that this technology stuff is real and the curves are easy to extrapolate. Unlike the above discussion about charting, these are things which *can* be extrapolated pretty reliably ;-)
I don't believe this has anything to do with a new battery technology, but hey, it might....
yes- I agree with your talk-down position and a good cautionary note. The price reduction is largely not a new chemistry or battery breakthrough situation. Of course that means it's more assuredly going to happen. I will note however a couple of special cost reduction adders that give the GF a (large) edge in that regard. Tesla batteries are already starting cheaper than any currently available, so the next step down he's talking about (30%+) is from that level, not what others are at currently. That's a harder nut to crack that the current industry reductions. In addition, nobody has really leveraged supply chain ground up through full pack in a single large factory-sourcing-operation utilizing the latest production methods, eliminating middle profits, using solar to cut costs of factory, etc/ etc. The resultant 30-40% achieved on top of current tesla batteries is going to be beyond what others can do- regardless of using the same basic chemistry.
Also, with stationary storage, I surmise they are actually adjusting the chemistry (not changing the basics, but adopting some new proportions) that cut even further (50%) for that application. I suspect the 2 location start for 1 GF is a head-fake and they'll end up doing 2 in a stagger. Bottom line- I agree with your cautionary assessment, but relative to current competition (and 3 years from now), Flux's we're gonna wipe the floor is pretty accurate I think