Bohemond had a target, he had authorisation from the Pope, his expedition was quite large, and endorsed by powerful rulers in the West.

Don't all of these factors apply to William the Conqueror's invasion of England as well? But surely William's conquest of England was no Crusade.

I'm unfamiliar with the specific case you mention, but it strikes me that some religious motivation beyond Papal approval is necessary in order for a given expedition to qualify as a Crusade. In particular, I think it is necessary that the expeditionary force view the invasion as part of a Holy War.