Technically it is a bug - cPanel assumes you can have two (2) Postgree databases and two (2) MySQL databases - which adds up to 4 databases total. On free-hosting accounts there is no Postgree databases available - but cPanel does not recognize it is not part of the package.
Free-hosting accounts have two (2) MySQL databases. You can however reuse them for more then one script (CMS) - separating each script's tables with a unique prefix - this is unfortunately only an option if you do the install manually - Softaculous can not handle you specifying a existing database.