True, but in that case I would argue that it was a smart decision.
They didn't have a product in the smart watch category, wanted to pounce and get the biggest market share. They pre-announced, got people excited, and therefore people started holding off on buying smart watches (i.e. killing part of the competition's sales) and create a massive hype around the product when it launched for sale.
I don't know if this was the strategic thinking at Apple, and don't claim to. For all I know, they may have been experiencing major manufacturing difficulties that stopped them from launching the watch on schedule.
But what i do know for sure is, they have never pre-announced the sales launch of one of their existing products, because they know that it would immediately kill off all sales of said product until the new version is released. It makes no sense whatsoever for Apple to announce the rMBPs in June, and launch them in september.
Either they announce at WWDC and launch within a 2-week to 1-month window, or they wait until the product is ready to announce it.