ASA - Batter/Runner touches 1st thinks ball is dropped and heads towards dugout

[hohlernr]

This play caused quite the controversy tonight:

Runners on 1st and 2nd, batter hits flyball to centerfield. Centerfielder dives towards the fence and just barely misses the ball. At this point the batter/runner has run though 1st base and thinks the ball is caught and heads towards the dugout.

The batter/runner never leaves the field, but ends up near the 1st base dugout before he realizes what happens. By that time the ball makes it in the infield and first base is touched and the runner is tagged (for good measure). All hell breaks lose after this as the umps have no idea what to call. They eventually agree that since he never made an attempt for second, he's basically free to do what he wants and is safe at first. I vehemently disagreed, but to no avail.

I can't find a clear ruling in the rule book, what was the proper call?

Thanks!