BJT circuit with base emitter shorted
The 2N2222 is maximum rated at 30V for V\$_{CEO}\$ and, considering the circuit says the line voltage can be between 20V and 50V then maybe this circuit is a design to test the breakdown voltage of the 2N2222.

However, figure 40 in AN70 does show it being used as a zener to prevent over-voltage being applied to Vin on the LT1533 - there is no strong evidence that this is a properly tested idea. Sure the 10k resistor limits current into the 2N2222 but it's not a design technique I'd recommend. Just use a 24V zener I would suggest.

You can't rely on the 2N2222 not zenering at 50V and maybe this might exceed the LT1533's Vin value. I'll check....

The LT1533 has a recommended Vin limit of 24V and a maximum rating of 30V so I'd say this was a bad design without strong evidence to the contrary.