" I think we'd normally be a bit scathing about cars ignoring Road Closed signs (e.g. Russell Road), so isn't this just the same thing for peds?"
I can see exactly where you're coming from, but I think there are some major differences.
The main one is that a driver ignoring a road closed sign would be breaking the law, whereas pedestrians walking into the road is entirely legal.
Also, when a road is closed there usually isn't any other option but to route cars round the houses, whereas here the lane is down to one and a half anyway, which in reality means only one line of cars, so a tiny reshuffle would give space for a pseudo pavement.
Also when a road is closed a diversion is signed, whereas here there isn't one noted for pedestrians.