Whenever you are using “U” in UX or UI, it usually is in reference to some interactive media. If you are using the term “user” to describe the audience of static media, that’s confusing. If the “audience” isn’t interacting in ways other than turning pages or playing videos, I wouldn’t use “user” to describe anything.
Last I checked, InDesign is mainly for static media. But when it comes to electronic display, there’s an in between state where the file isn’t as static as print or as interactive as widgets on a page. This might be something like animations, slideshows, or e-books. The information I gave you about generating assets was more about developing user interfaces for software, kiosks, or web pages where you do more than just turn pages or play videos. It involves graphic designers working with programmers.
If he’s talking about using powerpoint or keynote, it sounds like he’s talking about multimedia design. That’s slightly different from software development. I haven’t done stuff like that in a long time, so I don’t know what’s best to use these days. But I still wouldn’t call that UX/UI design. I would call that presentation designed for audiences, not “users.”
For your own marketability, I would learn how to develop on as many software apps as I could get my hands on as long as I didn’t have to pay for those apps. But if I had to pick one for each type of development, it would be illustrator for vector, Photoshop for raster, InDesign for static layout, and maybe Adobe Animate for multimedia. I’m assuming you probably have more export options from Adobe Animate, but I haven’t used it. All I know is that it replaced Flash which I did use a lot.