No, the theme is not "collectibles" and will still be announced on the start of the jam.  The collectibles from what I know is just like an extra challenge for the jam.  You will still base your game on the theme announced and required to add "collectibles" to it.  Example the theme is Adventure and you made an action platformer, if you put example like coins in the game then the coins is your "collectible".

1. The jam focus: (this time "collectibles") is required (mandatory)

2. The jam theme: is optional (not required), "but it is a voting category, so you will score higher overall with a good use of the theme"