My old Speer #10 handloading book shows several standard-pressure 158 gr lead bullet loads producing around 950 fps out of the 6" test revolver, which should equate to between 800-850 out of a 2". This was using the cannister-grade powders of the day. Using specially blended powders (not unusual for cartridge mfr's) to optimize results for snubbies is certainly possible,so I think their claims are quite likely true or at least not exagerated too much.
We'll have to take BB's word for the standard pressure, but the velocity is easy to check if you have access to a chronograph. Has anyone here chrono'd them out of a snubbie?