> PostgreSQL is released under the PostgreSQL License, a liberal Open Source license, similar to the BSD or MIT licenses.

https://www.postgresql.org/about/licence/

MySQL is also licensed under the GNU GPL.

PostgreSQL however is not: https://www.postgresql.org/about/licence/

As I recall, at one point MySQL drew significant criticism (or at least skepticism) for being dual licensed and requiring contributors to relinquish copyright to their code. To many, it felt like the goal was to lure you in and then change the license model once you'd adopted it fully.

This was many years ago, before Oracle even entered the picture, but my guess is that that is what GP is remembering.