I just find it bizarre that you've assumed they were intending to use a different phrase and somehow managed to accidentally land on this one that means exactly what they were using it to mean, rather than having deliberately used it to mean exactly what it means.
Good thing that's not what I've assumed.
I'm suggesting that, like a lot of people, they're using words that sound similar but mean different things, and in this case, it would be very easy to make that particular mistake, especially once the American English and British English pronunciations of route (another related word) and it's derivations get into the mix.
At best, it was a bizarre decision - the natural language choice would be to use root out, because spies are a thing you root out. They're one of the commonest things you "root out". So why swap to a much more obscure/culturally specific usage which ends up meaning something similar? The answer I believe is "because you don't know better".
It's an absolutely an obscure Americanism - my wife is American and extremely well-read/educated and has never heard of this usage you're describing (as in "uncover"), though perhaps it's regional (she's from near Chicago). It's not as extreme as the other one they used previously though - I can't remember what that was but it was genuinely funny to hear someone with an RP accent say it like it was just a normal word (it was something like "caboose", but like, more obscure).
I guess there is perhaps an entirely alternative theory of the crime - that this writer knows full well what the correct British English would be, and knows full well that this is a weird thing to do, but thinks it's funny to make Imperials with RP accents say these words/phrase. The fact that it's happened before lends some credence to that approach.
EDIT - As a totally 100% pointless aside, I will note the baleful influence of Top Gear (specifically) has created a situation where a bunch of American journalists of a certain age (about 30-50) who write about cars use Anglicisms of varying extreme-ness routinely, so it's not a one-way street.