It regarded his professional work on GitLab: https://twitter.com/suprnova32/status/720396175954698240
I think it's completely appropriate that he link instead to GitLab for such a thing, and I think it's remarkable that he didn't think the same. This isn't like the ad world, where if your customer is Coke you can't be seen drinking a Pepsi in public (which I agree is crazy): he was posting about GitLab itself, linking to their GitHub mirror instead of to their own site, which completely undermines the GitLab position.