That is not my understanding of the deal, but if you have sources to confirm this I'm eager to read it
My understanding is rather the opposite: They lunched the "Tesla Energy"/"Powerpack"/"Powerwall" when they did just to ensure Panasonic that they had a marked for the cells from the Asian plants even when the cars would be would be served by the GF: "
See - we have a product that will use your Asian cells, and we have a marked for this. So please invest in our GF, we will buy all your cells for both the GF and your existing factories - as many as you may ever produce!". A few weeks later Panasonic confirmed investment in the GF if I recollect correct.
Edit: of course the "deal" may be worded like you suggested, and that is exactly why Panasonic were unsure whether they would invest if the GF or not, and needed this reassurances.