This doesn't strike me as a new 'attack' (I have to imagine there's even a name for such attacks), and 250 miles seems a large radius to 'deanonymize' someone, even a high-value target (even if such people didn't take any other measures to avoid being tracked...)

For reference, here's a 250 mile radius around Toronto Canada https://i.imgur.com/ydpR0IZ.png