Simple receiver unwanted selectivity
I suspect you have two effects that combine to give a peak in the response.

The antenna is physically short relative to the wavelength of the frequencies being received so it will act as a low value coupling capacitor between the transmitter and receiver - This will give a rising response @6db/octave.  The low input impedance of you circuit will tend to put the rollover point fairly high.

The amplifier itself will have a fairly low frequency response that will be falling at 6db/octave.  The main effect is probably caused by the 22k resistor and the base to collector capacitance.

The two effects combined will tend to give a peak at some frequency.

You don't say how selective it is - can you plot the response from say 1MHz to 10MHz?