The Psamtik doesn't use its main beams in that fight for some reason no, it's a reason why the techroom entry is the way it is 
However, it actually losing the fight is definitely a bug. Can you tell me what build you are playing on?
It's the most up to date stable release version of SCP, and v3.3.3 of Blue planet complete. I don't spend enough looking at the builds to give you more detail than that. If you can tell me how to generate a log for you i'll get that done.
In terms of the main beams, flying around the Psamtik is both retail and Blue Planet version its' main beam weapons are "unused" when targeted. I guess the devs intentionally removed them?