I agree with that. She did not take the threat as a substantial threat to her life, but she could, and probably did, interpret it as a threat of some sort.
This seems to be what happened:
She's violating park rules. He tells her to leash her dog. She escalates by basically telling him to piss off. He escalates by saying if she's going to do what she wants to do then he's gonna do what he wants to do but she probably "won't like it." Then she goes all racist and escalates by calling 911. I don't dispute that she is almost entirely the one to blame here, especially when she did the final race-tinged escalation. But what he said was one step in the escalation. So he's not simply someone who informed her of park rules and watched her go all crazy on him.