That is correct. Before digital technology, almost all Professional uses Nikons, including NASA for the space camera. It makes sense that NASA keep using Nikon.
By the way, NASA also uses hasselblad.
The point is, a lot of people are getting into digital camera now and since Canon is the biggest player in the market at this moment, many mistakenly think Canon has always been better than Nikon. But those who uses camera long before the digital era knows Nikon "was" the best camera maker.