No, ATOM is not a Fallout game. It's a great post-apoc cRPG, with Fallout inspirations, but it's still not a Fallout game.
Calling ATOM a Fallout game is diminishing the Fallout and ATOM games. Just like calling STALKER a RPG is diminishing STALKER and RPGs.
The RPG system in Fallout is very different from ATOM, the character system is also different, the setting is extremely different (one is retro futuristic, the other is just retro), factions are different, the universe of the games are different, the way the games play is also different even though they are both good turn based cRPGs, the lore has nothing in common except that civilization as we know it ended, and the list can go on and on and on.
I would love to have Van Buren and I would love to have ATOM 2. But I wouldn't want my Van Buren to be ATOM 2 or vice versa. It's good to have variety, and both Fallout and ATOM have plenty of differences in design, writing, character generation, world, lore, etc. that they make two good cRPG series.
We don't call the Firefly tv series Battlestar Galactica and vice versa, why would we call Fallout, ATOM or vice versa too?
ATOM deserves to stand by it's own laurels, even if it was inspired by Fallout, as much as Fallout deserves to stand on it's own laurels even if it was supposed to be a sequel to Wasteland. Doing the opposite would just be detrimental to the ATOM name.