Eh, it's hard to tell from this blurry image, but it's possible it's more like "WATCHOS" (with the "WATCH" part in the stylized small caps that they've been using).
Good call, I guess it probably is all lowercase, then. I hadn't seen the WWDC app.If you download the WWDC app, they're also referring to it as 'watchOS' there - I've just downloaded it and attached a screenshot below. Though it could be stylised in their marketing, I think the general name might shift to 'watchOS'.
I have been calling it wOS since theWatch forum opened (or maybe before). Only makes sense when we get to 2.0 and I bet that will be it next year.