A virus is a specific type of malware but for the general public is broadly synonymous with malware. Ask the average user, and the commenter in the OP screenshot, what the difference is without looking it up and they can’t tell you.
A virus doesn’t need to be spread broadly for it to be concerning, impactful or dangerous. Often these attacks are very carefully targeted at the victims.
A vulnerability is generally exploited by a virus to inject code by either modifying memory or files the target program relies on. One such vulnerability was
With this vulnerability it was possible to modify any file on a Linux device, meaning viruses would be simple to implement and deploy. Many android devices are still vulnerable.
To think that all possible vulnerabilities have been fixed, or are known to linux developers, would be extremely naive.
Furthermore a virus is often targeting a specific application and while OS level controls restrict the avenues of attack it doesn’t prevent flaws being introduced by developers.
You’ve already been given a list of viruses for Linux, if you’re genuinely so concerned with defining them by impact you can look them up. You have the information needed to do this yourself, and it is not my responsibility to educate you, though I do seek to counter misinformation where possible.