Tā zài yéye shēngrì shí xiě le "fúrúdōnghǎi" sì gè dà zì.
He wrote the four characters 'fú rú dōng hǎi' for his grandfather's birthday.
Tips
culture
Classic birthday/longevity blessing, almost always paired with 寿比南山 (shòu bǐ nán shān, life as long as Mount Nan). You'll see this couplet on red banners at older relatives' birthdays.
history
Recorded in the Ming-era huaben 《清平山堂话本·花灯轿莲女成佛记》: "寿比南山,福如东海" — a stock auspicious phrase for centuries.