"There's a little bit of Autism in everyone" ?
The problem with that statement is that it completely disregards and minimises the lived experience of Autistic people.
I'll try to explain.
I think the comment comes from another problematic statement: "Autism is a spectrum" which, from what I can tell, most people seem to think means some people are only a little bit Autistic and others are a lot Autistic. Not true. Autistic people are all Autistic and may have some challenges in common and some that differ than others. (Like all people, yes? I mean, not all women live the same lives....)
I guess assuming that some people are only a little bit Autistic lets us feel we can relate to Autism in some ways. But is that our place?
Lets take sensory overload as an example. Sensory overload is not something that only Autistic people experience. I am not Autistic. I do experience sensory overload sometimes. My daughter is Bipolar, not Autistic, and she experiences sensory overload sometimes too. Which means, in some small way, we can relate to an Autistic person. I don't see that as a problem. It's OK to say to an Autistic person that you can understand a little about what it is like to experience sensory overload, if you do.
But that does not mean you know what it is like to be Autistic and it does not mean you have a little bit of Autism in you.
Here's another way to look at it. My daughter is Bipolar, and experiences depression sometimes. I experience depression sometimes. I can relate to some aspects of my daughters experience. But I do not know what it is like to be Bipolar, nor am I "a little bit Bipolar". I just know what it is like for me when I am depressed. Some of that may be similar to what she experiences, some of it is not. If I claim my experience with depression means I know what it is like for her to be Bipolar, I am dismissing her lived experience and making light of her challenges.
If someone says they think everyone is a bit Autistic they are dismissing the lived experience of Autistic people and making light of the very real challenges they face living in a world that by and large does not accept them as valuable and is not set up to support their needs.