[He could prevaricate. He could soften it, make it sound less fanciful. He's hardly kept secret of his current "job" since getting here, though, so instead he'll simply explain with an entirely straight face:]

Well, after I lost most of the use of my hands in a car crash and Western medicine failed me, I went to Nepal and learned how to harness magical forces previously beyond my comprehension. These days I'm in charge of guarding a sanctum designed to help generate a shield that protects the Earth from extradimensional attack.