However at the moment it is unavailable to be selected as it says that the option will be made available soon. We can’t be sure of when exactly in-store pickup will be made available, but the fact that it is now listed does hint that it should be coming soon. In fact a report from last month suggested that online purchases are expected to carry on through May.
This seems to suggest that come June, it could be possible that Apple will start making the Apple Watch available for in-store purchases, kind of like how you could walk into any Apple store and buy an iPhone, iPad, Mac, and so on. Of course this will depend on Apple being able to churn out enough product to meet the demand.
For example recently it seems that Apple has become overwhelmed with orders of certain models, pushing their estimated shipping times to July which is admittedly a rather long wait.