As I recall he was trying to use Linux as if he was a regular non-techy person. So it could make sense for him to do that knowing it’s wrong. (Which wouldn’t apply to “apt install Steam” yes do as I say issue, which a regular user probably wouldn’t have tried and ignored the warning even with jargon there).

I don’t find it completly unbelievable even a techy could make that mistake because they do not use version control software like git.