in 50 years, someone link to that thread and point out "the inventor of cold fusion replied 'thanks linus' on the linux creation thread"
Not to be confused with Jeremy Allaire, who did not. :)
I'm not sure about that. Maybe Linus appreciated the encouragement. Depends on the person, but knowing that people like what you are doing can help motivate a hobby project.
They're talking about people who replied years later (i.e., today, apparently as a result of this post on HN or other sites).