Oh! This is actually really fascinating and something I've done a lot of research on.

There's a couple of different factors that are theorized to be at play.

To preface, I'm not a clinician. I'm training to be a therapist but I am not yet one and won't be for a while so don't take anything I say as gospel.

For starters, it's not your imagination, I don't have the stats at hand but there is a marked difference between neurotypical and neurodivergent people in terms of representation in poly/non-monogamy. To the extent that research in the area has been done, it does show that there tend to be notably more neurodivergent poly/non-mono people.

One of the factors is that being poly/non-mono generally comes after a period of introspection. Most of us came to that table after we went through some self-discovery and that process can also bring to light knowledge or awareness of neurodivergence. It's the same kind of process with discovering you're queer - it all requires some inward looking and doing that can reveal other things about yourself.

Another factor, specifically for ADHD, is novelty. It might sound a little crude but those of us with ADHD (myself included) have a different physiological relationship with dopamine and as such we tend to need novel stimulation more than most people. Poly provides for that by increasing the number of people that can be involved. ADHD people can fall into the "NRE junkie" trap for that reason (ask me how I know.)

Another factor is the poly/non-mono emphasis on open, explicit communication. This falls in more for the autism crowd (AuDHD represent) but mono relationships are generally built around a culture of unspoken understanding and if you are someone who finds those kinds of unwritten rules frustrating and hard to understand (as many of us who are neurodivergent do) then poly/non-mono dynamics can be really refreshing because it's built (ideally) around open, explicit communication of needs and wants.

Still another component is the "out group." If you're neurodivergent, you're less likely to feel like you "fit in" with more neurotypical people and as such you're going to be drawn to other people who are more in the "out group." A percentage of that population are poly/non-mono people and that increases the chances of you linking up with that dynamic. Same kind of reason why poly/non-mono tend to be more into or at least aware of kink than mono people.