Not necessarily, but I guess it depends how you define "dependency".

For example, it might be partial ordering is needed only, so B doesn't fully depend on A, but some parts of B must happen after some parts of A.

It also doesn't imply necessarily that B is consuming an output from A.

And so on.

But there is a dependency yes, but it could be that the behavior of the system depends on both of them happening in some partial ordering.

The difference is with asynchronous, the timing doesn't matter, just the partial or full ordering. So B can happen a year after A and it would eventually be correct, or at least within a timeout. Or in other words, it's okay if other things happen in between them.

With synchronous, the timings tend to matter, they must happen one after the other without anything in-between. Or they might even need to happen together.