Having the link to the Reddit page on the Imgflip image page is called cross-posting. Probably more than one way to do it.
I think you have to have a Reddit account for it to work, not 100% sure about that. Make the image here, you can either use your Imgflip account (with your username displayed or using the anonymous option) or create the image on Imgflip without an account or while logged out.
Here's how I've successfully cross-posted. #1 Click the share button, #2 copy the highlighted link (what would be a click to show comment here on Imgflip)