calculation of torque constant based on bldc datasheet, getting different torque constants
It looks like that data sheet is for the current drawn from the 48V supply.  The torque constant of a motor applies to the ratio between the shaft torque and the current applied to the motor itself.  It's fairly close to the motor torque over a wide range of shaft speeds (in both directions -- torque vs. current is close to the same when the motor's acting like a generator as when it's acting like a motor).

The current drawn by the motor driver of a BLDC is different, because the driver (if it's decent) is a switched amplifier, so the current drawn is just the total power (motor shaft power plus any losses) divided by the supply voltage.