Prof Cullinan did refer to the genomic test, stating it needed further evidence of spread or leakage as to how they caught it at the hotel.
If one sequence definitely shows that it is a descendant of another then they will know even if they do not know how it was transmitted.
SIDE STORY:
When I was on my Croatian small boat cruise last year (oh those were the days!) there was a large USA three generation family on the boat too. Quite complicated with multiple previous couples, but with shared children, or half-children and one set of grandparents (quite wealthy who evidently paid for everyone's cruise).
One of the adult children was on the cruise as he was a biological child of the father on the cruise, but had only recently found him. How he found his father was that he had done a DNA test through AncestryDNA (the family tree group). This linked him with an adult female (also on the cruise) in Ancestry who he was able to contact and it turned out she was his aunt. From the aunt it was worked out that the brother had sold his sperm while at university to make money. It was anonymous. The brother also did a DNA test and that confirmed he was the father.
They were a very complicated, though also very friendly, family and the above was actually one of the tamer family histories of the group.
The genomic sequencing used with CV19 does the same thing. It allows when complete and especially with multiple samples from different people to work out how close cases are and order of descendance.