There is, I suppose, a line of thinking that if your work is ostensibly guesswork, you might eventually guess wrong. Maybe he’s just seeking some sort of reassurance at that level. Might even be worth levering it as a training opportunity.
For what it’s worth, my role is very similar. A very large part of my work day to day is “well, I don’t know, but I’ll see if I can work it out.” I’d rate my problem solving, troubleshooting and general lateral thinking skills as both stronger and more valuable than my raw technical knowledge.
I spend a lot of time getting dropped into the middle of directionless shitstorms where I have little or no experience of the technologies involved. I’ll analyse the problem, define it, and get wheels turning to resolve it. How I do that I couldn’t even begin to tell you, but I appear to be exceptionally good at it. If a manager asked me to explain it, I wouldn’t have a clue.