for a guy who can't monetize his followers to do. The fact is that 135k followers is not a huge deal anymore. I don't think McKinney did any shenanigans to get to the number. He just posted a lot of cool dunks that attract followers.
The fact is that Instagram followers can hard to come by for established brands. My company has 30k Instagram followers but has 10 times that on twitter. It's all about the entertainment value of your post on Instagram. On other platforms like twitter and facebook, the quality and depth of your posts are much more important. You can post funny videos of your dog on Instagram and hit 300k followers, this guy does:
https://www.instagram.com/dognamedstella/?hl=en