I think the term "vitrification" in this sense is coming from the pottery industry. I have never seen it used with the type of ceramic used for firewood. However the firewood ceramic parts are all fired to over 2000 F and definitely undergo a change where they become much harder, change color and probably become less permeable to water, but I'm not sure because they are still permeable after firing (a lot of the clay used in pottery is too btw). So whatever you call it, yes the firewood parts are properly kiln fired to very high temps.
The concern with ceramics is overblown anyway. Even vitrified or kiln fired parts can produce hazardous silicates and other particles when they are ground up, but the issue is quantity. People who need to worry are people who are in regular contact with dust clouds that they can breath in - for example people who mine stone, people who grind stone, dirk bikers or anybody riding a vehicle frequently on dirt roads where there is a lot of dust, people who live in desert where there are frequent dust storms, etc. Those people need to use proper protective equipment to be safe. The amount of ceramic dust that can be produced by a vaporizer on the other hand is less than what you would breath in after a slightly windy day at the beach... the beach is nothing but a ton of silicate particles rubbing against each other (sorry a ton is actually a massive under exaggeration). You probably have already breathed in a larger mass of silicate particles in your lifetime than exist in all of the firewood's ceramic parts (and those aren't in particulate form). I wouldn't worry about this, I honestly really don't think there are any concerns with the safety of ceramics in any vapes.