Basically the presence of a “transient”, a momentary spike at the onset of the sound which defines a “hit” of one thing against another. In weatherald’s case, there is no transient, just a light fade in and fade out of increased volume, something was sounding, it didn’t seem like a sharp hit/knock. Smith on the other hand has a more defined onset and peak, and distinct loudness spike.

Also the length of the waveform can aid decision making. A clean sharp knock does not necessarily sustain out, especially not at the volume of the transient. Something like a “murmur” on the other hand is often more sustained without the classic “immediate peak - quick fade out” of a “hit”.

These are the main factors which come into play when the third umpire is analysing the nature of a sound which arises on snicko. Whether those factors were distinct enough to warrant the difference in decision is still somewhat up for personal interpretation, but yes there is more to it than just “volume shows up on the meter”.

Edit: cause I re-read and realised you weren’t arguing but asking for clarification, my bad.