Perhaps video exist of him blowing them out in one breath to show how strong he is, but I doubt he had the strength.
He may be gripping the table to steady himself in the chair.
Dementia causes the shakes.
I recently attended a birthday party for my daughter’s father-in-law’s 80th birthday. They had a stand with 80 candles in it, and he had the grandkids come and blow them out.
Biden could’ve had Kamala blow them out.