Enough (I don't know what the ratio of upvotes vs flags is) users flagged it. Based on comments I'd say most saw it as a lame press release both in timing and how it was worded. With big news (the main github discussion thread has 1200+ comments) that can happen. There's no agenda by HN admins to suppress an angle. More upvotes from other users cancel out the flag.
In the next couple of days I'm sure there will be more articles, press releases and lots of (medium.com|blog) thought pieces coming out addressing gitlab's position. Like https://news.ycombinator.com/item?id=17225725
You have 450 karma right now. I think the flagging featured gets enabled at 500, can't remember.