I haven't yet worked out a plausible reason why the Russians would have aided the US's hoax space program, but I found some magic mushrooms in the garden today, and I have high hopes they'll do the trick.
The US also hoaxed the launch of their own rocket in 1968 (OV1-13) with a fake radiation instrumentation package. After a 13-month hoax mission to measure and map the Van Allen belts, they hoaxed having the certain knowledge how to pass an astronaut through the belt unharmed.