A frivolous, possibly disparaging metonym, contrasting English football clubs Salford City with Manchester United, alluding to geographical location, i.e. Greater Manchester, and the prominence of the colour red on their home kits.
The witty lexical choice and alliteration of βminiβ insinuates that while Salford play professional football (EFL League 2), they are not as illustrious as the more prominent Red Devils, especially in the context of more intimidating clubs meeting with the Ammies in knockout competitions, e.g. the Carabao Cup, FA Cup.
Perhaps, the most evident logic behind the epithet is the fact that six of seven owners of Salford were former Man United players.
βLeeds cant sic beat mini man united π β β @najminazari984, 30/08/2023 (YouTube comment)