Hugh did not answer his phone as he was otherwise engaged when she called. When he did answer it he returned the call right away, and if Marce was nearby likely told her about it.
He was completely uncertain what Arnica is, and probably mispronounced it at least two times (Arnaca, or arcica?) while talking to her. Of course he'd want to help, but he doesn't know if he's the best person for the job or not.