From the IBM employee's perspective it should seem reasonable that if he's asking for specifics that take time to figure out and for answers to questions while not contributing anything to the project, that he should pay for those answers in a timely fashion for his benefit. He's treating the Github like a support page so I don't see anything wrong with the maintainer offering a support contract in response to that. It would be beneficial to both parties.
If the maintainer said "I'm not releasing this until you grant me a support contract", maybe that would be extortion. Until then, he's simply getting the service he pays for.
If the maintainer said "I'm not releasing this until you grant me a support contract", maybe that would be extortion. Until then, he's simply getting the service he pays for.