I don't think they were vigilantes but abusers who had been harassing him over his race/disability and took it to the next level, using suspected paedophilia as an excuse. In a similar way as racists in the American South used to accuse black men of raping white women as an excuse to lynch them.
A family statement, said: "It should not be forgotten that Bijan had been the victim of hate crimes for a number of years before his death, both due to his race and his physical disability.
www.bbc.com/news/uk-england-bristol-24724534
It would be convenient for the authorities to go along with the anti-paedo vigilante idea, as they could avoid having to admit they had race/disability hate crime on their hands.