My first reaction/interpretation was indeed modes of travel, but ... "Travel photography" also includes images of the places you visit, different cultural things, people, you name it.
As David had to go into hospital, he may not be able to clarify it, but he also says 'be creative.' So, be creative and interpret the brief as you see fit.
As usual, as they say, the voter decides.
But then, as Jeff says, What do I know?