Hola Gregorio. *Como* has a number of different meanings. When it's used as a conjunction, it can mean "as," "since," or "because." That's the way it's being used in the sentence you cite. I went over to the WordReference.com site--by far the best place I know to get information about Spanish vocabulary, grammar, and usage. I put in "como," and I got lots of different uses, one of which was the following:
2 (porque) as, since
*como llamó tan tarde, ya no me encontró*, as he phoned so late, he didn't find me in
Here, *como* is used in pretty much the same way as in the sentence you've cited.
I hope this helps.