Some small speakers simply filter out sub-bass. Others faintly reproduce it. Then there is the more rare situation of this speaker where it puts out the sound at reasonable volume but it is distorted.
Seems like different words to address Frequency Response and distortion.
Something like, deeper frequency response than expected for a small woofer with increasingly high distortion. I am thinking tuned ports and resonance. I am beginning to prefer sealed enclosures for small woofers
Filter is not the first thing I think of when I see a woofer rolling off at lower frequencies, specifically I suppose that is correct.
This is the 6 ½ inch Peerless woofer that I use on my desk. Note no port resonance or noise. See attached.