An off-duty firefighter has been arrested in Hong Kong after surrendering to police over alleged common assault, the South China Morning Post has learned, following a viral video showing him shoving and shouting at a young couple in a Mong Kok shopping centre.A source familiar with the matter told the SCMP on Monday that the 48-year-old man, who said he works as a firefighter, turned himself in at Mong Kok police station on Sunday, accompanied by his wife.“The arrestee admitted that he had acted that way as he suspected the [other] man ... had intentionally bumped into him,” the source said.The arrest followed an online backlash against a 24-second video, posted on Instagram on Saturday, showing an altercation between a middle-aged couple and a younger couple at Sim City shopping centre in Mong Kok.In the video, the older couple accuse the younger pair of bumping into them at a crowded escalator entrance.The video begins with the middle-aged woman saying she did not squeeze herself into the younger couple.The middle-aged man, dressed in a striped green T-shirt and wearing a green cap, then shouts at the young couple at close quarters, accusing them of bumping into him and his partner.