700 miles is around 1127 kilometers... which I'm sure you knew and were just highlighting that US flights ain't that much longer than EU flights on average, but it's worth noting for clarity that they are indeed longer.
Yeah for some reason five years ago it was significantly lower than today, it's gone up to around 850 miles now. Not that I can tell you precisely why, but that's what the stats say.
Not really. For US in 2018 it was ~700 miles (https://www.bts.dot.gov/newsroom/2018-traffic-data-us-airlin...), and for EU in 2020 it was ~1000 kilometers (https://www.eurocontrol.int/sites/default/files/2021-04/euro...).
There are a lot of short flights (anything not coast-to-coast or north-to-south, basically) that skew the average.