Yes. Human activity can probably cause volcanic eruptions, albeit indirectly. Regardless, human activity affects volcanic disasters in several other ways.
First, let's look at how humans can cause volcanic eruptions.
Humans affect climate, and climate affects volcanos
Kutterolf et al. (2012) showed recently that climate affects the frequency of volcanic eruptions, chiefly through changes in global sea-level and isostatic effects. Ice unloading can also trigger eruptions in places like Iceland, as researched by Sigmundsson et al. (2010). So it seems highly likely that human-caused climate change will affect the frequency of volcanic eruptions, although according to one of the scientists:
We predict there's a time lag of about 2,500 years," [co-author] Jegen said. "So even if we change the climate, you wouldn't really expect anything to happen in the next few thousand years."
The lead author adds:
The impact from man-made warming is still unclear based on our current understanding.
Clearly this climate cause is rather indirect. And certainly the extent to which it's an issue today is open to debate. As you suggest, there may be some others causes. But, either way...
Humans affect disasters even if they don't cause them
Humans can contribute to disasters in other ways than being the root cause of the natural phenomenon. They are relevant to how natural phenomena affect humans; if they don't affect humans, we don't call them 'disasters'. Think about things like the following:
- How we educate people about natural hazards that might affect them.
- How we design early warning and emergency response systems.
- Where we choose to build our dwellings.
- Where we build transportation and other support systems.
- How we manage forests and farming.
Read about hazard evaluation, monitoring, and avoidance, for example around famous recent eruptions. Some of these, such as Montserrat, are especially well studied. This BGS page has some more info on that volcano.
A couple more things
Humans almost certainly had something to do with a mud volcano eruption, which displaced thousands of people in Indonesia in 2006: the Lumpur Lapindo eruption, which is coming up on its 10th anniversary. Read my article from it's 8th birthday, and see this question. Obviously, this is a completely different kind of volcano.
If you want to start an eruption, Erik Klemetti (a legit vulcanologist) has some tips.
Kutterolf, S., M. Jegen, J. X. Mitrovica, T. Kwasnitschka, A. Freundt, P. J. Huybers (2012): A detection of Milankovitch frequencies in global volcanic activity. Geology, G33419.1, DOI 10.1130/G33419.1. Read more.
Sigmundsson, Freysteinn, Virginie Pinel, Björn Lund, Fabien Albino, Carolina Pagli, Halldór Geirsson, Erik Sturkell (2010). Climate effects on volcanism: influence on magmatic systems of loading and unloading from ice mass variations, with examples from Iceland. Phil. Trans. R. Soc. A 2010 368 2519-2534; DOI: 10.1098/rsta.2010.0042.