Hi & welcome!
Agreed, though I do think there may be a historic truth there, from settlers in covered wagons wanting to try to grow roses in their new locations. Sticking the cutting in the potato could keep it from desiccating for some time, possibly having taken root by the time the trip has ended. Although it may have sometimes worked, there's nothing about doing this that would cause it to be a preferred method for attempting propagation, unless your cutting does need to spend a few weeks in a covered wagon. This old tale has gone viral for some reason this spring, but should probably remain a discussion about history, and example of the determination a gardener can have. :+)
Roses do take root easily from cuttings though, stuck in the ground about 6" deep. You can also ground layer them by bending a branch to the ground, lay a brick or rock on it to hold the stem in contact with the soil, ignore until root ball has formed under rock/brick.
IDK about the viability of rose stems obtained as bouquet entities. There's probably some florists who visit here. Hopefully someone with that kind of experience will pop in & help out on that.