This is just a guess but I believe it might be measuring the number of connections in the past year. Why I think this:
the numbers are too high to be weekly (billions of connections vs. ~150M passengers per week)
the numbers seem to be roughly similar (2-3B) on most servers regardless of age so it doesn’t seem to be an “all time” stat (the one exception I saw was Fornebu which has over 5B connections – nice job Fornebu?)
2.5B connections is about 50M connections per week which seems plausible