So when you spend a very intense fifty days chasing down someone that culminates in The Worst All-Nighter Ever, followed by roughly ten years of looking into cleaning up that same person's mess, their face is kind of burned into one's mind.

So when Jotaro realizes that the person he's yelling at looks a lot like Dio, and sounds even more like him, albeit younger, it gives him pause. It's not just his voice, either, that kind of pompous arrogance takes him back to that night in Cairo pretty quickly. His first thought that this is some more Stand-related bullshit, but that makes no sense. He would know nothing of a younger Dio for a Stand to draw upon to make this illusion, if it is an illusion.

There's a short moment where Jotaro draws a breath, then sighs to himself with a brief closing of his eyes. Trying to sort things out and considering the possibilities of Stand tricks within Stand tricks makes him truly realize just how fucking weird his life is, and how much he needs some asprin.

Less worrying now, more curiosity later. If this is indeed Dio, he obviously does not recognize Jotaro, which hopefully means he doesn't want to kill him for being himself.

He starts moving again, glancing back at the blonde young man with similar annoyance as before. "Do what you want, but I'm not slowing down if you don't keep up!"