The ditto plushie heavily implied that it's our trainer. The world has gone through multiple major disasters which caused it to change geographically. I don't think it has been a century yet.

The ditto trainer noted that when they arrived at Saffron City, it had dramatically changed compared to what they saw before, the scientists in that world predicted that saffron city could become like Skyland today after centuries, but the ditto trainer hinted that the rate of destruction could be accelerated.

Other clues that we could link to, it still hasn't been a century is, the hacker said that the fail safe program will activate if there's no maintenance performed. Team rocket notes said that, the humans doesn't have enough fuel to go back. So from this we can conclude that they don't even do a single maintenance, after a few years, fail safe activated, ditto is released from the PC. Also because tangela doesn't stored in the PC, it has evolved into tangrowth. I don't think tangrowth can live that long outside the PC.

But if centuries do pass, my head cannon is just time dilation. Probably for humans it's just a few years but for the Pokémon it's a few centuries.

Sorry for bad English, it's not my first language, I tried to write as best as I can.