Grealish tapped home the Three Lions' final goal from close-range as they despatched Iran 6-2, marking the moment with a broad smile as he stretched his arms out to the side and rolled them in in waves.
Far from being a flippant or spontaneous reaction, the Manchester City forward was keeping a pledge he made to 11-year-old Finlay, who has cerebral palsy.
Finlay wrote to his favourite player earlier this year, referencing Grealish's close bond with sister Holly, who also has the condition.
"I wish there were more people in the world just like you who treat people with disabilities the same as anyone else," Finlay wrote.
Grealish followed up with a letter of his own and also made a surprise visit to meet Finlay in person at a football session run by the City In the Community programme.
It was there that he pledged to dedicate his next goal to Finlay, who initially suggested the more challenging dance move 'the worm' before settling on the arm gesture Grealish recreated in Qatar.
"First of all I've got to try and score, then I'll do it for you, but I've only scored once this season," Grealish said, in a video captured by the Premier League.
"I'll do it for you, I promise, next time I score."
Grealish took to Twitter after the victory over Iran and said: "For you Finlay," alongside a clip of the original video and a picture of his celebration.