Of course, simply riding your bike normally causes winds that vary from 0 to 35 mph or so (if you've got some hills around or are really fast.) That doesn't cause strange readings in any GPS I've used, though I've not used the 510.
Even if you're also throwing in gusting "real" winds I wouldn't expect much of a difference.
HOWEVER, strong winds are caused by air moving from a high pressure zone to a low pressure zone (really, all winds are, but weaker gusting winds are often locally caused by thermals), and tend to indicate changing weather. So it may very well be that the barometric pressure changed considerably during your ride, that the pressure dropped and that was seen by the barometer as you gaining 600 feet more altitude than you really did.
To be sure, you might be able to look up the barometer readings for that day, if they're available on an hour by hour basis, and see if it was going down? You could also download your data to a computer, and compare the recorded altitude to the altitude for a given location as given by a topographic map. (This one might require some work.)