He's probably referring to a month or two ago when they came out of beta. They relaunched the website, changed some features, added some big new games, etc.
Except, when they did it, the page just went down with no warning whatsoever. They left a message on the screen that made it appear like GOG was going out of business, and that people would somehow be able to download the games they had purchased later that week. This took place immediately after a big sale, and people who had just a few minutes prior been making last minute sale purchases were unable to download the games they had JUST purchased.
A few days later, it was announced that GOG was actually only coming out of beta, they weren't going out of business, etc. They took the site down for a week (presumably because they were making server upgrades) WITHOUT WARNING, brought panic down upon their customers (going out of business? OH NO), and then when it was all over, released a video basically laughing at those people and saying they were "sorry" that their customers didn't "get" the joke.
A message of "Hi, we just removed access to your legally purchased games for a week because we thought it was funny" has not endeared them to a lot of people.