There is only one possible way they could do it on purpose. Easter egg (for the fifth time). Why else wouldn't they say it in the tech room. Also, it is physically impossible to fit a Helios into a myrmidon in a way that it can be shot (IIRC). FS2 might not necessarily be physically correct, but they don't just put stuff that are so obvious in the game as a serious thing. Oh, wait! It wasn't obvious! For one, you'd never think that a Space Superiority fighter would be able to hold AC bombs. Two, Not one single canon mission allows you to fly a Myrmidon and have the Helios accessible. And three, you would either need to go into the tables, create a mission, or use a campaign to figure it out.
I could understand them doing it by accident, though. It'd be a bit hard not to catch it when checking over the tables, though.
EDIT: I gotta stop using the word 'though'