Creepy guy.

I was walking through a park on my way to school and this guy walks up behind me, and kind of walks past me quickly. I see that on his phone he has a picture of a naked womans private parts, and he is tilting the camera specifically so I can see.

I walk slower so he can walk infront of me and just overtake me but he keeps his speed slow too. At the exit of the park he stops and tilts his phone even more to make sure I can see the photo on his phone, I just really quickly speed past him and call my dad when am a little further away from him. I kept checking behind my back and the guy just dissapeared - I don't know if he was following me covertly or what.

Is this a trafficking tactic or something? I am really creeped out because I have never seen something like that anywhere. Has anyone ever had an encounter like this and what happened to you guys after (if anything did)?

(This is a repost, og got taken down bc wall of text).