The milage calculator indicates the miles you will earn if you had flown TK (not other airlines) and receive the TK business class bonus, only the standard miles are used for calculation for other airlines.

If you look at the website, you can see the break down:

The standard miles are: 1,594
The Promotional miles (bonus if you flown TK): 557 (That would depend on your TK status - higher status gets more promotional miles).
Total: 2,151

As you did not fly TK you'll get only the standard miles times the multiplier for business class on SQ which would be 135% or 125% depends on the actual SQ class (I assume U or D based on what you got in the end).