Then why could his trusted "winning team" focus on IR? 
Actually, I don't think, the flashgun is emitting IR patterns, just red ones. And Fuji as well as Nikon MILC appear to not activate the focus help patterns. I think you're right with IR sensitivity of modern sensors, but just to the point as most cameras feature an IR filter. In front of the sensor. And DSLRs don't AF directly on sensors... But then, using IR film back in the made "defocussing" always necessary. The little red mark on film lenses was the focus index if IR film was loaded. Which then means: IR focus position and non-IR focus position is different. And I doubt today's lenses will act differently?
Actually, I don't think, the flashgun is emitting IR patterns, just red ones. And Fuji as well as Nikon MILC appear to not activate the focus help patterns. I think you're right with IR sensitivity of modern sensors, but just to the point as most cameras feature an IR filter. In front of the sensor. And DSLRs don't AF directly on sensors... But then, using IR film back in the made "defocussing" always necessary. The little red mark on film lenses was the focus index if IR film was loaded. Which then means: IR focus position and non-IR focus position is different. And I doubt today's lenses will act differently?