Today I realized something kind of interesting...
The Motorcycle Gang at the Tubeline Bridge on Friday is called "The Black Empoleon Gang", which is weird since it's pre-E4 and it seems odd they'd be named after a random Sinnoh Pokemon that has nothing to do with motorcycles.
When you defeat them though, it's revealed that they change their name based off the first party member of your team...mine, at the moment, are called "The Black Emboar", and this seems to show that perhaps someone in the past defeated them with an Empoleon.
The only major character with a set Empoleon, as the DPt heroes will never have an Empoleon guaranteed, is Darach, the Castle Valet who uses Empoleon in every fight and his general design seems to suggest Empoleon due to its color-scheme.
Darach previously took care of Caitlyn, who is now an Elite Four member, and an interview with Nintendo Dream hinted that Darach is closer to her than it seems, suggesting that he may make an appearance in Gray (or the 3rd Version). So, basically, I think Darach, prior to the player, traveled through Tubeline Bridge on his way to see Caitlyn and defeated the Black Biker Gang with his Empoleon, causing a name change.
It's a theory I'm proud of thinking of.