I'm curious if they tested this in highly-congested cells, since that's when cellular modems have to do the most "magic" and probably hit weird implementation edge cases. I think using the C1 in a packed football stadium is the real test of whether Apple has caught up to Qualcomm.
Other than mmwave (which this modem does not support), I don't think there's much more magic to do in an empty vs. a congested cell for a baseband.
5G spectrum is managed by the network, so the only thing that will happen is that each device will get shorter/narrower time/frequency slices, but there shouldn't be any unexpected cross- or same-channel interference of the type that is common for unmanaged protocols like 802.11 or Bluetooth.
