The first question you should be asking is "what percentage of the population in the immediate area of that ICU is vaccinated?" If 85% of the population there is un-vaxed then you would expect 85% of the patients to be unvaxed. You can't go by "national" rates - health care is provided locally and it is not uniform.

It is well known now ( even Fauci has had to admit it) that the vaccine confers only a partially effective protection against infection, against hospitalization and against death, and that protection wanes.. so the next question to ask is - how long ago were most people in this area vaccinated. If it was 1-3 months, then the vaccinated may be temporarily better protected than the unvaxxed.

Third, your brother's friend may be concerned that he will loose his job or be otherwise punished if he speaks the truth .

Fourth, if this is one of the "best hospitals" their ICU may be a point where critical ill patients from elsewhere are transferred.. so depending on how those transfer decisions are made, the unvaxxed patients may be selected for ( and that may be because they are more likely to be sicker)