I've seen this with ships that don't have the types of weapons they're expecting. For example, a vigilance that has a phase beam but no missiles, seems to still try to act like it's long-range support, rather than short-range assault.
Hmm. That's all but impossible - the ship's entire conception of its role is based on the weapons it has. It doesn't know that it's a "Vigilance-class frigate".
Possibly the target was very scary, so the ship didn't want to engage at all.