This is not so much a current mirror, as a level-shifting inverter. In this circuit the U2 boost converter produces +5V from a pre-existing
-12V source.
This 5v is expressed across R8, sensed by Q7A which has a base biased one EB voltage drop below ground by Q7B and R11. Due to simple transistor action, R8 current (minus Q7A base current) flows in R10, providing a feedback voltage for U2 that is referenced to the -12V rail, on which the internal U2 voltage reference sits.
RL