As the title says, this is a WordPress post with a comma separated tag. This is done using a WordPress filter, are you interested in the code?
/* WordPress filter for tags with commas * replace '--' with ', ' in the output - allow tags with comma this way * e.g. save tag as "Fox--Peter" but display like "Fox, Peter" * or "cafe--restaurant" for a tag "cafe, restaurant" * * Follow me on Twitter: @HertogJanR, https://www.saotn.org */
You can find the function code and explanation in my display commas in WordPress tags blog post on Sysadmins of the North.