I thought fallout was post apocalyptic with a retro-sci fi theme, don't see western.... maybe a bit in Fo2 with Redding.... but they mixed so much stuff in 2
It was always a sci-fi western. Sci-Fi western doesn't mean it's not a retro futuristic post apocalyptic though. The retro futuristic post apocalyptic actually works perfectly in case of Space/Sci-Fi Westerns. Because it makes a perfect world for the whole Western genre. Which is what I quoted up there, the definition.
I finally found a definition for Sci-Fi Western:
A science fiction Western is a work of fiction which has elements of science fiction in a Western setting. It is different from a Space Western, which is a frontier story indicative of American Westerns, except transposed to a backdrop of space exploration and settlement.
A science fiction Western occurs in the past, or in a world resembling the past, in which modern or future technology exists. The anachronistic technology of these stories is present because scientific paradigms occurred earlier in history but are implemented via industrial elements present at that time, or because technology is brought from another time or place.
So as you can see, it fits Fallout 1 perfectly. It occurs in a world resembling the past (people making new/recent settlements, shortage of resources, trading caravans including water trader caravans, sheriffs, cattle, tribals, outlaw/raider bands, most settlements are very low tech, etc), in which modern or future technology exists.