Iterative development is a software development model that was trendy before agile. It was, itself, intended as a contrast to waterfall development. It is, essentially, the idea that you don't design something and implement it, but keep designing, evaluating and re-specifying as you go. It works well with the idea that deployment is not the end of the process, though you can have that with waterfall as well - you just go back to the top of the waterfall after deployment.
Agile is really, to my mind, a refinement and extension of iterative development. It specifies that iteration in the form of frequent prototype and semi-functional deployments and ongoing contact with clients.
Now, the quote says that DevOps aligns with these two development models. That doesn't necessarily mean that it combines both. DevOps is another development model, and that statement is saying that it has fundamental points in common with agile and iterative methods. Basically, if you like or can do iterative or agile, then you'll fit into a DevOps workplace without too much trouble. That is what it is saying.