I did know they were ranked number one but it surprises me nonetheless. Belgium got knocked out of Euro 2016 in the quarter finals and the semi finals of the 2018 World Cup. France got to the final of both and won the latter. But then I have absolutely no idea how the FIFA world rankings work. I think it's a complete mystery to most fans.
Here is how it works:
https://www.goal.com/en-us/news/fifa-world-ranking-how-it-is-calculated-what-it-is-used-for/16w60sntgv7x61a6q08b7ooi0pSo it is based on a combination of:
1. Raw result - win, draw, loss
2. The quality of the opposition
3. The significance of the match - friendly, qualifier, euro (or equivalent finals), world cup finals.
4. Overall strength of the confederation - e.g. UEFA, Concaf etc.
It doesn't surprise me that Belgium are top as they lost just one game in the World Cup finals (to the then top ranked team and they beat Brazil on the way), having won their qualifying group with 9 wins and a draw (only bettered by Germany in Uefa section).
Since then they've recorded 16 wins, one draw and one defeat going into the match with England at the weekend, including a 100% record of 10 wins in their Euro 2020 qualification tournament in which they scored 40 goals and conceded just three (the best qualification record across all teams).
Since Martinez took over as manager in 2016 they've won 36 or their 47 games with just 7 draws and four defeats (and that includes Sunday's against England and a defeat by Spain in a friendly in his first game in change).
Sounds like world number one form to me, unless you can think of a team with a better overall record. France are, of course, second in the rankings.