Exactly that. I assume they didn't have many clothes and possessions then. They must have taken no more than a large suitcase/duffel bag each, plus a rucksack. It wouldn't be possible to walk, or even travel on the tube with any more baggage than that, realistically.
It doesn't sound like much stuff for a few years of living in London. People take more on a week's holiday!
But then, perhaps they were going to do it in two trips or multiple trips?
Richmond, Surrey to Bromley-by-Bow E3 is a pain in the a$$ journey, but it can be done on the tube. It'd be the cheapest way, just a few £ on an Oyster Card, but it could take up to 1.5 hours. No need to change lines, the district line goes all the way between these two locations.
Or perhaps they weren't transporting their clothes and possessions?
Exactly this. It doesn't make sense. Or were they doing a moonlight flit? I wonder if it was planned to leave their home or they HAD to leave quickly? It all went wrong when AC left the train (either to visit someone for something for himself and his travelling companion or because AC wanted to escape from his travelling companion). The small amount of baggage and big effort in moving home via The Tube (Underground) after two years of living is something to bear in mind as 'strange'. JMO MOO