Actually that is still the case. He said "de facto" not "official". Imgur still represents the majority of image links on most subreddits.

https://www.reddit.com/domain/i.imgur.com/

r/all shows more imgur links than i.reddit: https://www.reddit.com/r/all/

Your article dates from half a year ago and they still couldn't snuff imgur out with built-in upload facilities, suffice to say, as far as the users are concerned, imgur is the defacto beloved service. People on twitter are more likely to use twitter's img upload than redditors are to use their own.