This is probably just guess work, because in the past with new console launches, accessories tend to ship before the launch, at least with third-parties this isn't super uncommon. I remember specifically back before Wii launched, Madcatz basically had similar type of information, and the Wii ended up launching November 2006 in the US.
But I think basically everyone assumes the Switch 2 could come anytime in 2nd half, and September is just as good a guess as October is. But I'd guess an October launch if it's planned for fall. It really just depends on if they need to wait for their big flagship launch game to be finished, or if the the game(s) is already done and they could launch any time, and they are just waiting on timing the hardware perfectly so they have enough inventory for the holiday season.