My 2012 E70 X5 user manual says it measures wheel rotation speed to work out of the tyres are flat. The OP says it's a 2013 E70 X5 so it may have changed, but I think that's the same model. The link you have is for a BMW 5 series not X5. On mine you have to correctly inflate the tyres and then tell the system that the tyre pressures are correct and drive it so it learns the speeds. It never tells you actual pressure,