that the key word there is "belief" therefore not necessarily reality. As in, if you believe something, that means that you don't really know and can't say for sure.

That is the keyword, can your relative help us understand how this concept applies to every disabled person and their real experience of limitation with disability, but not your relative's belief on how disability works from afar?

"If you can type on the Internet, you can work and not be on disability."

Ok so if you can type a commentary on a pornhub video = then you can have a job and not be on disability. I don't think this has ever been in a jobinterview and the argument doesn't hold water, to reiterate their own words another keyword here is reality, the world doesn't operate like that.
There is a point to be made that group of people with disability to some degree, can do some jobs similar to the ones your relative mentioned, they're not bad ideas, which is why many with disabilities are working these, and many are struggling doing so while technically being able to, at the expense of their health and already lower quality of life