I recently queued up for an ARAM (All Random All Mid) game and instead of being given the choice between three heroes, all of the players could only choose the same hero. This must be a bug with the RNG (Random Number Generator) that caused the heroes available to not be actually randomized as well as the check for the same hero being available in multiple selections for the same player to have not worked.
This is intended.
Not a bug.
This is a feature. Randomly it will load into all same hero mode. When in all same hero mode it will randomly pick an eligible hero and use it to populate all selection slots. Not all heroes are eligible, for example Abathur is not a valid all same hero target even when he was still an eligible ARAM selection. I forget the exact list of eligible heroes, but it usually exempts heroes that are extremely degenerate or out right broken when everyone is using them.
This feature was disabled for quite a long time in ARAM mode. ARAM mode originally had it when it was still part of brawl mode, but some time after turning it into its own mode the feature was disabled. It remained disabled until a year or so ago when they decided to enable it again for some reason. I guess it is like how they have re-added brawls back and fixed up the PvE ones to now function again, maybe its removal was not entirely intended.