How did he start the game with a laser pistol? Cheat? Mod? 

he just started the game as marine with energy 1, I believe (that will grant you a free laspistol).

so it seems. also, getting heavy 1 grants a free grenade launcher. strangely enough, getting standard 3 will not grant a shotgun or a pistol.

yeah, it's one of those "how the heck have I been missing that for all those years" things. still, it's true, a marine can start with arguably the strongest weapon in the entire game. but do note that it won't help you much, as on medsci and engineering, there are almost no grenades to be found, and they are too expensive to buy in replicators (unless you play on easy), so you won't be really using the launcher until you reach hydro.

the laspistol is a nice bonus though, especially against those pesky droids on engineering (as that is exactly the part of the game when a gun with free ammo really comes in handy).