Mediterranean maybe (although I'm not sure), but it's actually very hard to find a ship, even as large as an aircraft carrier, in the ocean. The empty space is just too big. Satellites have hard time taking pictures of every square mile of a sea to find any ship, yet alone the one you need.

Sure, but there's a big difference between using nation-state resources like spy satellites, and using a public API exposed by a fitness app.

Not everyone can use spy satellites, and even if we're only talking about nation-states, many (most?) countries do not have spy satellites.

We couldn’t find a commercial jet (MH370). Both, while it was still flying in the air and after it was presumably lost in the ocean. They couldn’t track it in the air nor can they still find its remains after looking for it for so long. This problem is not trivial.

Yeah id be more impressed if he found a submarine using strava

If they have ships in the area sure but picking it out of the ocean if you don't already know where it is on satellite data is a lot harder. Until the last decade or so satellite tracking of ships visually was essentially the domain of huge defense budgets like the US that had more continuous satellite coverage. It'd be interesting to see how well that could be done now with something like Planet and tracking it forwards in time from port visits or other known publicized pinpointing.

> seriously doubt there is a country on earth which lacks the capability to detect an aircraft carrier

They probably lack the ability to figure out which specialists are on board.

Maybe stupid question but how would Iran do it? They don’t have any ships in the area and also don’t have any satellites that could take pictures, right?

Or does getting told by Russia count?

Isn’t the point that if you can identify one naval vessel by this means you can probably identify many?

If Charles de Gaulle turns off AIS, how does North Korea find it?

Why make it easier for them?

I think people tend to lack imagination about how some piece of intel could be used by an adversary.

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.