With the tristate output, it could be used as a level shifter by tie-ing the input low, put a pullup to 3.3V on the output, and enable the input to bring the output low, disable the input to let it go to 3.3V for the SD card high input.
But a passive pull-up is not as efficient as using driven outputs. (A fairly low value of pullup would be required to absolutely guarantee timing tolerances are met, and often we don't have good figures for capacitance of the circuits being driven.) If you are going to use passive pull-ups, you might as well use the hokey resistive voltage dividers that some people use.
No, they just tie the enable low (so the output is always enabled) and they feed the signals through from A-Y. They operate the 'AHC125 at Vcc = 3.3 Volts, and take advantage of the fact that the 74AHC125 inputs are 5-Volt tolerant. Note that many chips, including 74HC125 (no 'A' in the middle of the part number) are not 5 Volt tolerant when they are operating at 3.3 Volts. For the 'AHC125 note that maximum input voltage is specified to be 5.5V, not the Vcc+0.5V (or, maybe, Vcc+1.5V) that is typical for 3.3 Volt devices that are not 5 Volt tolerant.
For my money, I can't understand why (oh, why) anyone would use the '125 as a level shifter (even though it's not strictly illegal) when the '4050 chips are explicitly designed for level-shifting and buffering operating conditions. (What happens when your purchasing agent, hoping to save a buck, orders 74HC125 instead of 74AHC125 parts? Stranger things than that have happened. Believe me.) The last time I bought a few, the '4050s were cheaper, too.