It's an aggregate of the months you're selecting (2019/04 - 2020/03). If you select just March you can see what they're seeing:
https://netmarketshare.com/?options=%7B%22filter%22%3A%7B%22...
https://netmarketshare.com/?options=%7B%22filter%22%3A%7B%22...
I'm curious to see if they stick with it, or switch back to Firefox. I like how the article talks as if it was some sort of inevitable milestone we've all been waiting for. And now, instantly, the second that Edge finally eek-ed past Firefox (if we consider desktop usage only), it will never change. It will just keep climbing and climbing onto browser dominance :)
Pretty lame article if you ask me. Not very interesting.