Hypothesis: microclots are caused by the viral spike protein. The mRNA vaccine produces the viral spike protein. Therefore, a non-zero percentage of microclots are caused by spike protein originating from the vaccine.
One of the working theories on people suffering long COVID-like symptoms after receiving an mRNA COVID vaccine may apparently be related to spike proteins found in the patient's blood far longer than is typical/intended. This is apparently similar to long COVID patients.
At least, that's my layman's understanding when I was following it some years ago. I'm not sure if there's been more recent studies that have found more concrete links since then, but I suspect GP is in the same boat, which is why they asked.