The implementation of the algorithm didn't rely on it, but they did test it using that data.

>However, we did compare the Blocklist data we gathered with the sites identified by our algorithm, and we were very pleased that the preferences our users expressed by using the extension are well represented. If you take the top several dozen or so most-blocked domains from the Chrome extension, then this algorithmic change addresses 84% of them, which is strong independent confirmation of the user benefits.

edited: to respond to abraham's post directly

There's a difference between training with that data and testing against it, which is precisely what I wanted to highlight here since many expected Google to use such data for training. You can't do that since you can overbias/over-fit given what little daat we, plug-in users, are able to produce versus the amounts they have access to.

2nd edit: it should also be noted that that 84% figure they mentioned related to the extension data is a measure of recall. Assuming Google wants to do a better job with precision in these cases (don't want to get many false positives), that recall is still fairly good in mind since I'm sure there's some noise in that data.