This was often called this growing up. My ex-wife said I was first 1 or 2 months but recognized clearly much better than anyone apparently but she was very smart herself. There are always areas where someone know more than others then there are things like people knowing clearly why the decision is bad but do it anyway like with cigarette smokers which I'm one of (though 95%+ I use the vapor).
What I mean is I usually don't say much at all, even when people are showcasing their ignorance I choose to keep my thoughts to myself because it will likely be doubted anyway. People doubt things I read here at DU or anywhere but I don't ever make claims unless I'm pretty sure it is true. So they figure it takes me awhile to understand something said, in conversations mostly but I had a 111 GT score (high enough to qualify for a Warrant Officer) and generally above average scores. Generally most people I've known are passive aggressive so in coded conversations I understand it though it does get confusing for me to figure out when someone is being genuine or telling me some BS because they think it protects my feelings when lies bother me a hell lot more than the truth. The main thing that is baffling is the assumption made as to knowing what I understand or don't understand inside my head. A lot of times, an assumption is made as to why I say something so they respond accordingly and try to clarify and another misunderstanding so sometimes I chose to stop trying to clarify and let them think whatever they want to think.
I guess slow could mean various things so there could be something else behind your use but the context or the assumption behind the use I hear from other people directed about me is the thinking is not as quick as the average person (though they have no idea what I'm processing) or imply as not very smart which maybe I'm not but most of the time it was used as a way to bully. I do often take away to weigh the options before making a decision that a lot of times I over-think myself to a not doing anything as a decision.
Also head injuries, trauma, CTE, TBI, etc cause a lot of confusion, memory loss, symptoms similar to dementia basically that could probably consider the person "slow" but is it their fault or need to be weeded out?
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