True, but I'm also saying that Instagram had 13 employees at the time of being bought out. I don't have any numbers of users they had at the time but I know they had 1M+ new users on their Android launch. Which makes me assume a large iOS crowd.

If we figure that the engineer count scales linearly to the user count (which I don't actually think is true), then you've just justified twitter having 2,600 engineers. That is, if Instagram had 13 engineers for 1 million users. (they likely had less engineers but more users though).