"MySQL was also potentially faster as it did not implement all features of the SQL standard. "
This is a not great start. I assume it refers to MyISAM which has not been relevant for over a decade at this point. InnoDB made different design than PG decisions and was (and perhaps still is) faster at point lookups.
Well, the poster explicitly talks about 2003 here: „ In 2003, MySQL was much more widely used than PostgreSQL. MySQL was also potentially faster as it did not implement all features of the SQL standard“
This is a not great start. I assume it refers to MyISAM which has not been relevant for over a decade at this point. InnoDB made different design than PG decisions and was (and perhaps still is) faster at point lookups.