How are spammers doing this?

Somehow these bots they're creating are getting more adept at commenting. You'll read a paragraph that sounds original and completely relates to the news story you're reading. Like a comment on an explosion read something along the lines of "hey guys if you smell gas, it's okay to call the fire department to get it checked out. I'm tired of hearing that there is no jobs. Visit blahblahblah website. I've just started noticing this in the last week or so. It took a while before I realized it was spam. Pret-ty clever guys.