Riddle doesn't often have dreams- he typically has nightmares- but whenever he does, he welcomes them with open arms. He'd rather have a confusing dream that makes absolutely no sense to him than wake up at two in the morning covered in sweat, shivering despite that.
This dream was... different, though. Someone he'd never seen before was in it. Someone who drew him in, intrigued him beyond what should've been normal.
He hadn't seen them beyond the first few glances because he wasn't able to catch up with them throughout the dream- like a wild goosechase.
But when he saw them in real life, in front of his own two eyes? He had to follow them. He had to talk to them, to get to know them. What has possessed him to be this... invasive? Curious? He has no clue. Perhaps it was the intrigue and mystery lingering from the dream.
Of course, he wasn't as sneaky as he thought he was, and he definitely wasn't following the dream figure far enough away to make it look like he's simply walking the same way as them.
They turned and noticed him, stopping in their tracks and giving Riddle a strange look. He doesn't want to scare them away- no, that's the worst case scenario- so he raises his hands, "sorry, I know I may look like a bit of a creep, but... I swear I've seen you before."