So I have updated that offending section to say:
To define a frequency and time range change the track to Spectrogram view, click and hold the mouse button at a vertical position that you want to be the upper or lower frequency boundary to be.
See the full updated page Here:
https://alphamanual.audacityteam.org/man/Spectral_Selection
Is that better for you? Does that make the actual behavior clear?
Peter.