Yes, that’s correct.
The images you upload into your Evolve course will be the “finished” versions, exported from any graphics program you use to create them, usually in JPEG or PNG format so they can be delivered quickly over the web. Those can be downloaded with the exported course and re-imported into another course, no problem.
What I’m talking about are the project files from apps like Photoshop, Illustrator, Premiere, Camtasia – the types of programs that MAKE the files you use in your Evolve course. If you have a professional vendor creating custom graphics or video assets for you, it’s good practice to get these source project files back from the vendor so you can make edits and updates to them yourself in the future. A few years down the road when you need to revise the course, make small changes, etc. – it’s much easier if you have these source project files because they’re easier to edit. The final JPEGS and PNG are “flattened”, which makes editing them later much more difficult. Also, those flattened files used in your course are often lower resolution than the original project files, so you’ll have a harder time making them larger in a few years when screens are all much higher resolution than they are now. These project files are never uploaded into Evolve, so they would not be included in any course export file.
Reputable vendors will give you these files if you ask, but often they won’t offer to give them to you because it’s a minor hassle to package them up and send them. If you’re commissioning a work for hire, you’re entirely within your rights to request them though.