If you consider it's 10 years later, and Hank McCoy has been shown to be a genius in electrical and mechanical engineering among other things, it's simply likely that Beast built them. After all, Magneto did have the blue prints on microfilm, when he stole them in 1973 as seen in DOFP.
Hank of course, built Cerebro, as well as the Blackbird (that exploded in Apocalypse), as well as Havoc's suit, Cyclop's sunglasses and visor, etc.
Mainline production of the Sentinel program had Government funding scrapped in 1972 prior to DOFP, and then Trask's company was shutdown following the end of DOFP, including Sentinel production. Unless it was started up again, but consider that the general world sentiment was that mutants are okay, or at least not a threat, that's not likely.
Also consider it's 1983, they have not yet gotten the technology to build a holographic Danger Room as seen in the old timeline X3 (set in 2005), so it's likely real robots.