The specific question was highly tied up into their interrogation of the Covid-vaccine induced antibodies affinity for the N domain of the spike protein. If they had tested unvaccinated sera they could have ruled out any enhancement based on the vaccine-induced anti-N domain antibodies, suggesting they need to look somewhere totally different (such as something unique to their pseudo-virus vector, which naturally wouldn't apply to SARS-CoV-2 in the real world at all).