TfL have been in touch to clarify things, saying:
The work planned by Transport for London at Liverpool Street Station, to demolish a bridge, was completed ahead of schedule last Saturday (29 December). Unfortunately, Liverpool Street Station remains closed because Network Rail, which is outside Transport for London's control, has not finished their engineering work on time. We advise passengers to check with National Rail enquiries for the latest information.
So now you know who to mutter about on the way home. Good luck!