Andrew Goddard explains why this may have happened in this article at Covenant
The first and irrefutable conclusion that must be drawn from these two documents is the shocking inadequacy of GAFCON’s theological resource group and wider leadership. To have produced a briefing paper claiming to summarise the changes between the Nassau and St Andrew’s draft covenants but actually comparing the St Andrew’s draft to a quite different document unrelated to the covenant (and which many of the GAFCON team were involved in writing) is an astonishing error. That nobody in the group (or among the GAFCON leadership which released it) realised that the claimed removals from the Nassau draft were therefore all fraudulent suggests an inexcusable level of ignorance about the covenant process on the part of all those involved in writing and then disseminating this briefing paper to the wider Communion. The authorship is unclear but either we have a very small number of people writing what claims to be a representative document commended by seven Primates or we have a large group which failed to spot this basic and serious flaw. I am not sure which of these options is I would prefer to be reality. Unfortunately this all gives the strong impression that the conclusion – “the new document is severely flawed and should be repudiated” – was already decided upon on other grounds.
The second conclusion is that the other response of the same team is therefore seriously discredited, especially if it was put together on the basis of the briefing paper or by people who had seen the briefing paper and not realised its basic error.