And so Sheridan to avoid favouritism appoints a man who worships him as his idol.
In Sheridan's defence I don't think he actually knew (or cared very much) what Gideon thought of him. I do wonder how Sheridan knew about the guy though. It's never been addressed if he was involved in either side during the civil war or if he was out serving on an explorer ship at the time.
Actually, maybe Jack Maynard recommended him? Gideon was still an Ensign in early 2259 so it's highly unlikely he'd be commanding a ship of his own just two years later.