I get that sometimes.
I never really know what to do with it though.
For one thing, I don't think I'm all that bright. Sure I know stuff that many people find mysterious and I can do complicated math in my head but I know people who are quicker, more versed, and just plain smarter than me. Of the people I know, I'm in the middle of the lower quartile in terms of smarts.
On the other hand, we all tend to underrate our own abilities.
The other thing is this association of being incomprehensible with being smart. Seriously? I can make utter stupid rubbish sound incomprehensible so what has that got to do with anything? If you don't understand what I'm saying that does not mean I'm smart, or that you are not, but that communication has failed to happen.
If I intended to communicate with you, then it is hard not to see that as a failure on my part. Don't tell me how smart I am - tell me where you lost the thread. Then I can improve how I write.
If you understand what I am saying completely and clearly, then that would mean I'm pretty smart.