I suspect cock up over conspiracy in this instance. I feel a bit sorry for all involved.
almondcakes Goldsmiths held an event commemorating the Holocaust last week.
I was at the meeting at which the motion to which you refer was discussed. The original motion specified several specific memorial events, all of which were European (thus ignoring e.g. Rwanda) and would have made events mandatory, which is not the SU's role.
People at the meeting suggested that the motion be redrafted to make it more inclusive, for example including the Transgender Day of Remembrance and non-European genocides.
An SU officer offered to work with the proposer on a new version of the motion but was rebuffed. The proposer then wrote an unpleasant and dishonest internet post saying that we'd refused to commemorate the Holocaust.