SPOILER:
The novel explains that Woltz invited Tom to ask him what it would cost him to settle the pending labor dispute that Tom referred to when he met Woltz earlier that day at the studio. Woltz didn't want an alliance with Vito, and especially didn't want to give Johnny the part. He was just interested in getting past the labor dispute.
True TB. In the film (and novel), Woltz's emotional outburst perfectly portrayed his failure to grasp the meaning of Tom's visit.
