The INterstellar Wars were Total War in the sense that civilians were targets and the struggle was one between whole states rather than a small professional force.
While many people would still be working in "facilitating" roles, keeping society running - the post still has to move, kids are taught, etc - the entire Terran population would be behind the total-effort, so Avery's comment that everyeon was in the Navy makes sense in both a broad meaning and a specific one - all "Travellers" would be involved with or touched by the war in some way, and most would be contributing in some way.
While many people would still be working in "facilitating" roles, keeping society running - the post still has to move, kids are taught, etc - the entire Terran population would be behind the total-effort, so Avery's comment that everyeon was in the Navy makes sense in both a broad meaning and a specific one - all "Travellers" would be involved with or touched by the war in some way, and most would be contributing in some way.