Frankly, I have to admit a great deal of doubt about Porre's acceptance of Dalton were that truly the case. Dalton might be able to show off some fancy magic but the Porreans are obviously not idiots--especially not if they can invent Grobyc. They would not be willing to trust him.
Furthermore, I hesitate to see how he would know about Guardia in the first place. I doubt he had any idea Crono's friends were time travelers, and there's nothing to suggest his portal that teleports Golems is temporal in nature. In fact, it is far more likely he was transported to some rock somewhere he stored the Golems or even to where Zeal once floated. Either way, the odds of his appearence in the Present are quite low, at best.
No, Dalton nor Magus nor anyone else we know is at fault. Porre must have become more militaristic thanks to something else...I'd suggest the Black Omen except that canonically speaking it never survived beyond 12,000 B.C., so...it's just unexplained....we'll have to wait till Kato decides to inform the Chrono community across the world.