In most comic storylines, Jimmy Olsen isn't a guardian. He's more often involved in reporting and assisting Superman rather than having a guardian role.
I'm pretty sure it's not real. There's no concrete evidence or reliable source to confirm its authenticity. It could just be a story someone came up with for entertainment.
One great 'Chris Evans and Elizabeth Olsen Fanfiction' is 'A New Beginning'. It's a story that combines their on - screen personas and creates a unique adventure where they team up against a common enemy. The character development in it is quite engaging.