The time lapse video proves in of itself it's a volcano eruption. Ash clouds move much slower comparatively than a nuclear explosion.

A bomb is instant and that explosion is fully expanded within seconds. Eruptions are going non-stop for hours and as the time lapse shows you can see the sun set before the cloud is done expanding. Volcanic eruptions are also considerably more powerful than nukes, however the energy is pointed in one direction whereas a bomb's energy expands in all directions which is why again, people think nukes are more powerful than they actually.

Compared to nature, the nuke is still a cheap imitation.