Chris Parkin, 47, described “the most surreal five minutes ever” when the star and his girlfriend, actress Dakota Johnson, paid a visit to The Stag Inn in Hinton Charterhouse late Sunday afternoon.
The singer-songwriter jumped on the piano after a couple in the pub, currently planning their wedding, said their first song would be Coldplay’s A Sky Full of Stars.
“He just said, ‘Well, do you want me to play it?’ It was really brilliant, a brilliant moment,” Mr Parkin told PA news agency.
“It’s always a bit of a shock, things like that.
“It was one of those things where you go, ‘Okay, this happens’.”
In a video posted to the pub’s Twitter account, the star asks the pair for their names before playing his band’s hit song in the room.
“You never know who’s coming for a pint!” wrote the bill.
Mr Parkin previously described the moment as Martin walked into his pub next to Johnson – the daughter of Hollywood stars Melanie Griffith and Don Johnson – whom he did not recognize.
“I said, ‘He looks a bit like Chris Martin,'” he said.
“And his PA said, ‘Yeah, that’s Chris Martin’.”
“I had absolutely no idea (who Dakota Johnson was)… The younger girls in the kitchen were like, ‘That’s Dakota Johnson! She’s really famous!’”
Mr. Parkin also introduced Martin to his 13-year-old son Alfred, a budding pianist.
It was weird, but then again, brilliant – you know?
“He can play Clocks and can play several of their songs and he is classically trained on the piano,” he said of his son.
“And in fact, (it was) the only reason I stopped him… I said, ‘I hate all this camera-in-your-face stuff. But wouldn’t you just say hello to my son?’
‘And he just said, ‘Yeah, no problem.’ He was sweet.”
“It was weird, but then again, brilliant – you know?
“It kind of unfolded, it unfolded the way it does and you’re grateful when things like that happen, aren’t you?”
Mr Parkin said he had been to every Glastonbury since 1995 but having been absent in recent years didn’t feel he had missed this one thanks to Martin’s visit.
“It felt like Glastonbury was visiting me,” he added.
“I saw their first gig at Glastonbury and I’ve seen all the other Glastonbury’s they’ve ever done, so I’ve seen them develop a bit as a band.
“Love them or hate them, they’re part of British culture, aren’t they? That’s it right for him.”