[spudlyo]

We were excited to try a NoSQL db, having spent too many years using MySQL in ways that the designers of relational databases never imagined.

...

Given that we had experience with MySQL and knew it was adequate for our needs, it was hard to justify any other choice.

Agreed. It seems pretty clear from reading the article why they went with MySQL, which you wouldn't know from all of the Postgres butthurt in the comments.