Two beacons in one shot

I should consider myself lucky since I have a local 23 cm beacon to test my homemade biquad antenna. While aiming it, trying to discern reflections from the actual line-of-sight signal, the waterfall spread over 2 MHz showed another beacon, 500 kHz below the known one:

Without SDR I would not have noticed IZ1ERR/B. It was 10 dB S/N, even with the 23 cm dipole inside the house. We are in full line of sight, but it is pointing away from me (I am on his side)

I have recorded 50 seconds of baseband IQ signal with SDRSharp: if anyone wants it I will share a download link of the 404 MB file.