You are right to call out that the marketing to non technical consumers conflate these matters.
The clock that is being referred to, but seldom is a uurately, is the physical analogue symbol clock. Noting to do with network data, packets, audio jitter blah blah.
This is the clock that is used to synchronise the the transmission of the symbolised voltages through the twisted pair cables or fibre. This is the clock that is synchronised to by the peer host… and indeed the host has its own clock for its symbols back to the switch.
All of this really is irrelevant other than… and this is the key part.. this symbol clock if it produces phase noise, and all do to greater or lesser extents, this will be conducted, and coupled by the host interfacing electronics. In closed systems this will induce tiny perturbation signatures on powerlines and ground planes and even EF emissions depending on designs. This as we know through closed systems engineering principles will be added to the signal in the receiving where things like ground planes, powerlines and EF may affect audio circuitry… to the point where it is above the digital audio or analogue audio noise floor.