Single note dynamics for a custom soundfont

I'm using a custom soundfont for Violoncello and I noticed that single note dynamics don't work for it.But if I use the default soundfont shipped with Musescore 3.4.2 it works.
It has been stated in the mscore manual that for instruments supporting single note dynamics (e.g. strings, brass etc.), playback is also enabled across a single note or series of tied notes.

So the question is what does instruments supporting single note dynamics mean? (in terms of soundfont design not physically). And why isn't it possible to use single-note dynamics for a soundfont like the one included in FluidSynth for example?