Yup, I found about this when I accidentally clicked on such a link to PlayStore that was missing the colon and was confused when it didn't work and copy-pasted it in the address bar. I am sure it was just a typo on that website.

GitHub is full of similar typos in documentation and code files (74.8k results). I am not sure if there's a way to do a web search based on code and find "live" examples but I can't imaging there'd be a shortage of those either.

https://github.com/search?q=%22https%2F%2F%22++&type=code