Anything quantum is pretty difficult to grasp - if I understand this correctly they use error signals that they can derive from the classical information in the IP header to perform quantum error correction on the entangled photons to preserve the quantum state.

Entangled photons have the odd property to always perfectly (inverse) correlate when you measure their polarization. QKD uses this property to ensure that you can safely communicate a cypher key. Quantum with TCP/IP means no need for dedicated fiber as in this video. youtu.be/cWpqlgF7uEA?...

i would just assume it was impossible for the packages to go unobserved... especially over analog/copper, fibre only makes a bit more sense, but still...

This will only work on fiber and will require their "Q-Chip". The novelty is in recycling the TCP/IP protocol in this clever way. This is not something that can be run on existing networks but possibly in the future on existing fiber infrastructure with quantum repeaters in the mix.