Not sure why this is downvoted. I am not qualified to read the paper but I have the same question. My impression was that "long covid" was self reported and there is no way to medically confirm if someone is actually has "long covid"
We don’t yet know the underlying cause of long covid symptoms, which is what research like this is trying to uncover.
But if you say one has long COVID, you are describing a condition (possibly a new illness, but not yet?) with a wide range of symptoms that occur in different combinations in different people, it seems fine to ask for clarification about what sets it apart other than having gone through acute COVID (natural question, as a person who has gone through acute COVID can still subsequently fall ill with an illness unrelated to COVID).
It is sufficiently vague that I have the same question each time I see the term. Maybe this subthread-starter was sincere?
Plenty of cases of long covid are linked to not-particularly-severe covid cases.
"Long Covid" is extremely similar to other post viral illnesses that have been observed for decades, just getting more attention now.
But I didn't read the article.