I would call Savage and ask why the heck they put a 5/8-24 thread on a 223 barrel.

Should be able to be rethreaded, though you might loose an inch of barrel length if he can't get clean threads on the existing turned section and has to cut that section off. I'd still call Savage first though to see if they would warranty it. Sounds to me like a screw-up on their end where someone used the wrong program on the machining center when making the barrel. All of the outside machining (shank threads, contour, crown and muzzle threads) is done in one operation.