A legal transaction can still be considered stealing, and I think it's very easy to say that Xerox didn't realize what they were giving away. Now the thing is, when transacting with an entity like Xerox, it probably can't be considered criminal. :)
No, if you want to redeem the claim that Apple "stole" from Xerox you can't really do it based on the ideas that came out of those meetings.
The one thing Apple did that was vaguely disreputable is: they then hired away many of the key Xerox people. You can't say they "stole" the ideas but they did "steal" the employees. Not in the sense that it was illegal - employees have free will and freedom of contract and there was no non-compete clause - but that this went beyond what Xerox reasonably expected to come out of the transaction, so you can see how Xerox might have been miffed.