Well at least the base of Q2 operates at ultra low current, a few nA.
Q1 and Q2 act as a current mirror at DC. The current leading into the collector of Q1 is about 1uA. And that current is replicated at the collector of Q2. That means the current at the base of Q2 must be about 1uA/Hfe of Q2. A few nA.
Also the 1uA at the collector of Q2 is fed into the base of Q3 where it is multiplied by its Hfe, giving say a current of 300uA at the collector of Q3. You may be able to increase R2 or use an audio transformer in its place.
L1 and C2 form the resonant circuit and are coupled to an antenna some way of your choice.
The input impedance of Q2 under such low current is very high, however there is a lot of base emitter junction capacitance involved. That would cause a lot of phase noise if the circuit was used as a Regen detector but it is no problem for a TRF radio.
I built the circuit above, it works, but is not sensitive. The output volume is very weak. I'm driving a lm386 module at full volume. It receives powerfull stations in my area. I am using a litz wire ferrite antenna, which works great on a KM484 etc. if I connect a 2 foot wire to the coil, it works better, but not much. I am using 2N3904 and 2N3906. Tried various other transistors, all the sane result. The sound quality , while burried in noise, is good.