My guess (it would be nice if they actually said...) is that they were missing the required lang attribute on their HTML.
<html lang=en>
If not defined it will default to unknown (not to the user's locale) and so this makes Chrome guess. And there wasn't much text in the lightbox (which might be a different page?) for the browser to infer from.
That's probably true, however I'd be really curious to know why Chrome's guess for "yes" is the Spanish word for "Y-junctions" instead of the English word yes.
This was my immediate thought, but it doesn't sound like what they did. They also mention they still get the Google translate pop up - which suggests they didn't.
Though it sounds like they serve many languages, so they'd need to do each survey individually.
