It describes the sound as “...between about 7,000 kHz and 8,000 kHz...”
That would be 7 MHz - 8MHz.
I’m sure they mean 7.000 and 8.000 kHz.
Europeans use commas as a decimal point in numbers.
I checked it out and it is indeed centered around 7.5khz with a width of about 1k. A crude measurement with non-laboratory grade equipment/software, but that’s what I see.