Hello Paul. Thank you for requesting me.
It is physically possible to change the mileage on a vehicle, but most dealers and even shady used car lots would never bother messing with that. Besides being illegal, there's hardly a point. On your last question I ran your VIN through Ford's database which gives the complete warranty history and on the date and mileage of previous repairs coincides with the mileage you currently have now.
I would question the ambiguity of 'looks like it got hot'. Did they remove a valve cover and see discoloration of the head, or bluing of a camshaft, for example. I would also want a clear cut diagnosis beyond just 'needing an engine'
Head gasket failures especially on cylinders 2 and 5 aren't what I would call common, but I have seen them. This would result in coolant loss, white, sweet smelling exhaust vapor, and possibly the P2196. You're at pretty low mileage for that to happen, but it is possible. This can be verified by a chemical block test, along with cylinder compression and leakdown tests. On this engine, I perform all 3 before condemning an engine or head gasket. If the head gasket had failed, you would likely have a misfire code, or feel the engine run rough either at cold start, or when fully warmed up.
If you paid for a diagnosis, perhaps the shop can give a better explanation of what they suspect is going on, as it looks like right now we need more information.
I hope this helps.