That's not really the point. The issue is that a soldier almost certainly without a lot of thought ended up leaking information that he wasn't aware of leaking.

And furthermore identifiable information of a particular individual, which people can use to for example find out what unit he is deployed with, which may give you information about what the mission is about and so on.

In WW2 when transmitting morse code individual operators used to have what was called a 'fist', skilled listeners could identify and track operators by their unique signature. This was used during world war 2 to track where particular individuals and units were moved which gave people a great deal of information not just where but what they were up to.

If you leak the Fitbit information of a guy who foreign intelligence has identified as being part of a unit that's always involved in particular operations you didn't just give something obvious away but potentially something very sensitive.