I think he meant the difference between things being complicated (possibly unnecessarily) and complex (inherently). Simple things can be complicated to the level they're hard to understand, but it doesn't mean they are complex.
Yes this is what I meant. Perhaps I should've given a bit more context in my original post.
Here's a fun example. English has a lot of Latin and Germanic based words in it that you can construct entire sentences. I was surprised to find out as a non-native speaker. In my opinion, the Latin sentences seem way too complicated to express simple ideas.
Germanic example:
In my anger I struck my small sword in his belly.
Latin example:
In my rage I injected my gladius in his abdomen.
Complex -> complexity
On the other hand, complicatedness is a verb turned into an adjective turned into a noun.
Complicate -> complicated -> complicatedness
I read that as an implication that security concepts are not inherently difficult but are made difficult by people who explain it incorrectly.