@HenrikSchumacher you're right, they don't actually do it. But a lot of websites do it nowadays (if website A and website B use the same ad network, then website B may use your browsing history on site A) so when a coincidence that seems unlikely happens like this, one comes to think of that possibility. But it's not the case here, this really is a nice coincidence that they picked Mathematica over, say, MATLAB.