Yes it's a probable though very rare side effect (in the literature about 1 in 1,000,000), how does citing a rare case like that imply nobody should take a flu vaccine?
Some 330 people in every 1,000,000 die during surgery by the way here in the United States and the risk of a baby boy dying from effects of circumcision is 20 in 1,000,000 yet I bet you are circumcised as is your son(if) if there are any.
It is pure hysteria and superstition to take a case like your grandfather's and conclude that the flu vaccine is unsafe.