The answer is that it is almost a certainty that if a straight guy calls a girl out of the blue and invites her to a party he wants to bone her. He confirms that intent when, in the same convo, he asks if she has a boyfriend.
There may be rare exceptions, such as: the girl is, by way of disfiguring disease or accident, totally unfvckable and the guy needs a ride to/from the party and he is concerned about getting his *** beat by an extremely fugly (and hence insanely jealous) boyfriend.
Next question please.