Really?
Simple. It’s speculation on the part of FReepers about the cause of that holder’s blood clot.
The FReeper who posted about her sister has information directly from someone who suffered a clot, from something other than COVID-19.
holder = golfer
I think that the majority of FReepers are well aware that there are also other possible causes for blood clots. We all know that blood clots existed, e.g., in the 1960s.
It's just that no one cares about other, banal causes of blood clots right now.
Understandably, someone who posts an article about a young athlete getting a blood clot is going to attract a lot more attention from FReepers wanting to know her vaxx status. Almost no one is going to ask about, e.g., her use of birth control pills, or whether she had recently been travelling in an area affected by Lyme Disease, or whether there's a history of that in her family.
Understandably.
Regards,