Importantly, volcanoes are different in how they behave, depending on where they are in the world.
For example, volcanoes on the US side of the ring of fire tend to “belch”, like Mount St. Helens. However, on the far side of the ring of fire, volcanoes tend to be “brittle” and explode, blowing the volcano apart, like Krakatoa.
I doubt that it was a Krakatoa-like explosion, because such eruptions create noteworthy evidence around the world, that is sure not to be missed. For example, that explosion altered the level of the river Thames in London, on the other side of the planet, by almost a foot swell.
People all over the world knew about Krakatoa. It was hard to miss.
But compare that to Mount St. Helens or Mount Pinatubo in the Philippines. Both affected the world’s climate, but not in a very dramatic way, unless you were downwind of them.
Now, the *scale* of the cooling, as well as the “dry fog” would seem to indicate that perhaps *several* large volcanoes had “belching” eruptions at about the same time.
Say, if you had St. Helens, Mount Pinatubo, Popocatapetl in Mexico, or Mauna Loa in Hawaii and other such “new world” northern hemisphere volcanoes erupt at about the same time, all that the Europeans and Asians would notice is a “dry fog” and colder temperatures.
Or a volcano that erupted continuously for a period of time instead of just one big eruption.