The conclusion section of that very study says "...further research is needed to confirm these associations and determine causality and mechanisms" and "A causal relationship is plausible..." [emphasis added].
In other words there is an association, but the study is not able to prove (or even suggest) causation. For example, it does not exclude the possibility that other factors that actually cause autism and Tylenol use are themselves linked. So Tylenol use could be correlated with autism but not a cause of it. In that case, pregnant women who would otherwise use Tylenol not doing so are not reducing the chance of autism. And as the study points out, failing to treat conditions that warrant Tylenol usage can also have negative pregnancy outcomes.
Right, but there are plenty of things that can cause pain. It’s reasonable (although it also sucks) to tell women that they should avoid using Tylenol during pregnancy except for fevers in the short term.
As part of a scientific study, sure.
As general medical advice, no, it's not reasonable. Acetaminophen provides real benefits, giving up those benefits requires actual proof of harm.