There's complexity that comes with the problem domain. Then there's "incidental" complexity that comes with your choice of tools. For example, languages without garbage collection have more incidental complexity than languages with garbage collection: without GC, you spend a lot of time manually solving the problem of managing memory resources.
OO introduces a lot of incidental complexity. That's the point. It's clear, since he mentions some function programming languages, that he believes FP introduces less incidental complexity. I think that's exactly right.