Replying to Letter from my dead grandma

so my brother received a birthday letter from my grandmother today which contained a hand written note and a 20 dollar check. the weird thing is that the card was wishing him a happy 12th birthday, even though he is 26 and his birthday is in early april. the weirder thing is that my grandmother has been dead for 10 years, and the letter was postmarked at march 30th 1998. i guess it got lost somewhere in the mail system for over 10 years, and just got delivered now. he took the check to the bank just to see what they would say about it, and they wouldnt cash the check since her account is closed. it was very weird.