Where has my History proficiency come from?

The list of Proficiencies you have, aside from History, seem correctly accounted for by by your race, class, and background. Assuming you have listed all relevant information, there isn't any clear way you would have received this, so it is very likely a mistake.

Note that your "origin" is just a variant form of your background to provide roleplaying flavor, and in this case is not of mechanistic interest.

I do note that the "quick build" rules for a Paladin in the PHB suggest Noble for the background, and that a Noble receives History and Persuasion as Proficiencies. So if you, or your DM, or an automated website, had an early draft of the Paladin as a Noble before it was changed to Outlander, that might be one place where History was acquired and then mistakenly not removed.

It's probably a mistake

The details in your question rule out most ways of acquiring an extra skill proficiency according to the rules, in that:

• All your class/background skill choices are accounted for, so you didn't get it as a free choice due to overlapping class/background skill proficiency
• You don't get any skill proficiencies from your race
• You don't get any extra skill proficiencies from the class features you have so far
• You haven't multiclassed to anything that would grant new skill proficiencies (and would specifically have had to multiclass to Bard to be able to get a History proficiency out of it)
• You probably haven't taken the Skilled feat, which would give you 3 new skill/tool proficiences, or you'd remember that
• You probably haven't been granted training in an extra proficiency as a special reward (as described by the Dungeon Master's Guide) or you'd remember that

The background "origins" you mention are just a selection of possible occupations more specific than "outlander" to describe your character's background - they're purely a fluff choice, and have no mechanical ramifications.

It's possible that your DM simply decided to give you an extra proficiency for whatever reason, if they helped you make your character. You should bring it up with them and ask if you're meant to have this proficiency. In the worst case, you discover that you had an extra proficiency by accident (you're a new D&D player, and these mistakes happen) and the erroneous proficiency is taken away.