The 43-year-old rocker was taunted by local media, who shouted "Sacha, Sacha!" as they tried to take pictures of the person they thought was the 44-year-old actor dressed up as his football hooligan alter ego, Norman 'Nobby' Grimsby, reported Daily Star.
"It got a little embarrassing. Liam was in town to show his new Oasis documentary but a lot of the press here simply didn't recognise him," a source said.
"They just saw the hair and assumed it was Sacha dressed as Nobby doing another publicity stunt."
The pair have had a tempestuous relationship in the past, with Liam once threatening to "stab" the actor - who loves to mock celebrities - "in the eye".
Liam attended the fest with his girlfriend Debbie Gwyther and introduced the upcoming documentary about Oasis, which split in August 2009 following a string of explosive rows, at an intimate screening.