It's probably a significant amount of the deal guaranteed, making it almost a fully guaranteed deal. I would guess that something around 75% guaranteed would be considered significant enough to warrant that language. I could be wrong but if he's cut then I'm sure we'll hear more about that. I think he stands a good chance of hitting the guaranteed date because Houston's roster is incredibly thin, especially in the frontcourt.
Anderson had a couple of decent games in Miami after he was traded there last year but I think he's almost done as a player. He can fill the Eddie House type of bench shooter role though, bring him in and see if his shot's falling and if it's not then glue him to the bench. He's definitely not an a rotation player anymore.