That’s really up to you as the seller, although it’s not a bad idea to put something in your gig description that says if you offer it or not, and if it costs extra. There doesn’t need to be a Fiverr-set extra for that, you can create your own extras. Some categories have it because source files are extremely common in those categories (like vector design) but it can apply to others.
If you didn’t specify to the buyer that the source file was or was not included, you have the choice to give it to them or not. Some sellers would choose to never give the source file even for extra money because they don’t want their work edited. Some would choose to give the source file for free on every order and others will charge for it.