It is generally not intended for the Mechanicus to be the ones making first contact with a new race of Xenos. Brother Gentoo has the dubious honor of being stationed on Equus, for reasons that nobody can really explain, because the explanation was taken out back and shot by someone three or four links up the chain of command. Frankly, he's done this song and dance before. The Mechanicus are used to bending the rules a little to ensure that the Imperium's gears continue to turn.

This is how Brother Gentoo ended up being the one to make first contact with the inhabitants of Equus--a group of oddly-colored, unusually intelligent equines.

And then one of them asked him how lasguns work.