The context is the explicit tagging in this case. You don't need to understand language to detect English-as-a-second language speakers. (Indeed Markov chains will happily solve this problem for you.)

> they automatically model relations

No, they do not model anything at all. If you follow the tech bubble turtles all the way down you find a maximum likelihood logistic approximation.

I know, I know - then you'll do a sleight of hand and claim that all intelligence and modeling is also just maximum likelihood, even thought it's patently and obviously untrue.