I really think the girls would not have crossed the bridge or would have dialed 911 if they had a prior unpleasant/creepy encounter at the park with this guy.
It may be more likely that they just had a weird vibe about him. Plus, I don’t think the guy would have done something prior to scare them off.
Sad to say, if 13-14 year old girls called 911 every time an adult man made odd comments, stared at them too long, tried to talk in an overly familiar way, or scared them in public, they would be calling all the time.
The objectification of really young teens by adult men is real and it is widespread. And it often starts out by "friendly" talk - "hey, why don't you smile more?" "I'm just teasing" etc which are really forms of microaggressions.
I have no problem believing that something like @Tealgrove proposed is what happened in this case.