I mainly went off the report where senior USA advisors were being told of this fact by their Chinese counterparts at the back end of 2019.I don't know that 'deny' is the right word, there wasn't positive evidence. Interhuman transfer had long been strongly suspected.
Regardless, isn't it better to assume that it is transmittable? If you are later proved wrong, all you have done is mobilized a premature lockdown/restrictions on travel. Annoying, yes, but you haven't risked the lives of millions.