also to remember is there alien not human...
humans constantly strife to improve everything even if it works for many varied reasons most emotional
ie jealousy/greed/compassion/hate/friendship etc
the aliens may not have these motavations. so even if they have been in space for 3000yrs, whos to say they saw the need of improving bits of tech like guns etc. which as far as they might be concerned ,once at a level where they work in space and kill stuff dont need to be improved, same for ships,personal armour etc.
they could have invented interstellar drives etc because they need them now but are happy to use weapons that they have been using happily for 500 years