The term comes from combat - and if you want somebody to be killed quickly, you hold him up on the skyline where the enemy can see him and shoot him.
It was meant to be jocular - I doubt anyone's done that for real - but it was an option.
And as others have pointed out: this is a military vessel full of young people, not a cruise ship full of asthma-ridden seniors...and if they were truly so terrified of the disease, they wouldn't all be clustered together to give that very public and pointed show of support.
No, I'm sorry, I just can't imagine it was wise of him to try and use the media to do an end-run around his superiors.