To what? The author is specifically talking about making money directly from your app, which Instagram didn't do until recently (well after they released an Android version). And even then, it looks like their monetization strategy is to sell what appears to be a very limited number of ads-as-posts.
Instagram's monetization strategy was selling the company. That effectively required an Android version to protect and maximize their network's value.
I wonder if Instagram would have gotten more money if they'd embraced Android sooner (like WhatsApp).
Did you read the article? It's primary point is that there is more to the numbers than just the revenue earned via app sales because Android allows apps to use external subscription methods. It even cites a Salesforce CRM app as an example of this.