Does the timeline change for humans or for geology? If Henry VIII stays married to his first wife, and Martin Luther's 95 theses are accepted by the church, then I assume that all tectonic events stay the same ...
There's lots of tectonic events that HAVE been altered by human action. Take the increase in earthquake activity due to fracking for example. While the effects of medieval-era mining on stresses in the Earth's crust don't have as easily measured effects as fracking for natural gas does, I'm sure they have some effect.
The point is that volcanism is a chaotic system. Chaotic means that small changes can have larger effects (i.e. the 'butterfly effect'). For example, let's say that deep in the earth's crust there's an upwelling of magma, and there are two possible weak points where the magma could escape through and erupt. Say in OTL, one of those weak points was the site of a mine, and, because of this mine, that particular weak point was the weaker of the two, so the volcano erupted in a particular way. In another TL without that particular mine ever being dug, maybe the other weak point would have been weaker, so the volcano would have erupted in a different direction.
If a TL in which Henry VIII stayed married to his first wife resulted in a less prosperous Great Britain, then maybe fewer mines would be dug in a certain area, which would in turn cause volanoes to erupt differently. The point is that human actions (like mining) do have effects on geology. They're not drastic effects, but they are effects, and centuries and centuries of human action can change things like when and where a given volcano will erupt.
To be honest, I think it's perfectly plausible to write a TL in which all geological event go the same as OTL for centuries after the POD. However, in such a situation geological events are going the same as OTL
despite changes in the Earth's crust due to different mining patterns, etc. I think it would also be perfectly plausible for different mining patterns to result in different geological events, and I would not call a TL ASB because, in that particular TL, human actions had geological consequences. It's a fact of reality that human actions DO have geological consequences, and sweeping such geological consequences under the rug by calling them 'ASB' is simply unrealistic.