343 Industries was just created to handle all of the future halo games, Microsoft is simply publishing these games.
343 Industries has no history, because they have made no games yet, everything they pump out in the neer future will be Halo based, so it is all a mystery.
343 Guilty Spark, is the only hint we have because when sitting around and naming the company they could have possibly picked a name relating to the first project they were creating and the halo universe. And even that is a hypothetical.