It's more common for a maximum pressure to be provided than a minimum pressure, but 100 psi is in the ball park for a 25 mm tire. Continental's GP5000 recommends 95-123 psi for the 25 mm size (
link here). And their Gatorskin recommends 95-120 psi (
link here). Jumping over to Schwalbe, their basic Durano lists 85-115 psi (
link here).
Perhaps this is an older tire model, perhaps harkening back to when it was more common practice to inflate tires to about as high as they could go as a common practice?
Personally, I inflate tires (of any size) to a pressure that feels right to me. I generally run as low of a pressure as I think I safely can and still avoid pinch flatting and rolling a tire in a corner. I'm a 240 pound guy, and the narrowest I've ridden is a 28 mm tire (a tire which was really more like 25-26 mm fully inflated). I ran about 60 psi in the front and 80 psi in the rear. 70/80 psi on a 25 mm tire seems like a pressure I'd run, especially if I was any lighter than I am!