Yeah, it's really weird to me coming from the rest of the Internet to have random people I've never met say things like "Beautiful", "Great work", "I love it", etc., instead of, say, what you'll get in the comments of a youtube video.
Sadly, if it's just a single compliment with no relation to the actual image posted, it's likely a bot doing the commenting. This is a common way for people to boost their follower count.
That's all I ever see on my employer's blogs and announcements, and is far more depressing to me than any honest criticism would be.