And yes it is irrelevant. I do not control, perhaps do not even know what a roommate owns and vice versa. And that only pushed the needle up a but, to still being in the minority. You mention minorities? Gun owners are a minority
Households with "roommates" are a small minority of all households. About 40 million of 250 million adults live in a household with other people that they're not related to or romantically involved with. The vast majority of households that aren't individuals living alone are are families or unmarried couples. In those contexts, it would be typical for one member of the household to own the firearms as a legal matter, but others might use it or rely on it. For example, Breonna Taylor was living with her boyfriend, who was licensed to own a firearm. If the couple bought a gun for self-defense, it seems fair to attribute the gun to the whole household, not just the individual who purchased it. Or in another example, a parent might purchase a firearm that other adult family members in the household use for hunting or target practice.
You're also forgetting about voting. Gun owners are much more likely to be older, married, and live outside the city. (Many people who don't own a gun when they're young and living in the city purchase one when they move out to the 'burbs and start af family!) The same groups of people are also more likely to vote.