Basically, humans are pattern seeking creatures, and children exposed to white noise will try to find patterns in white noise, when there are none, thus leading to the brain maladapting to random patterns. My theory, but I couldn't find a good definition of traffic noise being related to white noise or classified in particular, but who knows.
In argument against your theory - a lot of parents use white noise explicitly to help their babies to sleep. From my own personal experience, most of those kids don’t then suffer from autism.
I used to share a room with someone who would fall asleep to TV. In the UK after the last show of the night there would be beep tone for a long time and then it would just be static, no signal.
This lead to me having a recurring nightmare which I also got for a long time into adulthood, seeing the tone as 1/2D line, flowing along nicely, and then the static would screw it up and turn it to knots and I would be unsuccessful in making it turn back to a line.
I have this same reoccurring nightmare and I also grew up in the UK.
The line would be smooth, but the violently contort into anxiety inducing sharp triangles.
This is the first time I have heard someone echo the same dream.
In a way perhaps it's kind of an abstract "powerlessness in the face of chaos" nightmare.
Not sure why exactly it went away. But I do remember being conscious of it in my 20s and trying to understand it. I think I tried to understand it consciously and accept some of the powerlessness perhaps. Or maybe later on, it was meaning general confusion and anxiety which was suppressed.
At any rate the nightmare was very scary and awful, as if something evil and wrong was there.