There’s a correlation, but not a causal link.

For example, lets say… A certain virus, that has a fever and headache as a symptom. If a pregnant woman contracts said virus, she likely will take acetaminophen for it.

Now, let’s also say, that particular virus can cause the markers responsible for autism to activate.

So, since the virus is unknown, the only correlation we see is the acetaminophen use, while pregnant.

Did the unknown (yet) virus cause it, or did the acetaminophen use cause it?