Strange circuit at power input
U25 transistor of pin 1,2,6 is connected to function as a diode such that pin 2 and 6 would be one E-B diode drop below VBUS.

Transistor of pin 3,4,5 with base to pin-2 would turn on when DCIN-5V is one E-B drop above. Thereby turning off the MOSFET.

The net effect is if DCIN-5V is higher than VBUS, then Q10 is turned off. Otherwise Q10 is turned on. Acting like an ideal diode with low drop out as you said.