In fanfiction, the author might be using this as a creative device to add humor and character to their interactions. Deadpool calling Spider - Man 'baby boy' could also be a way to show Deadpool's dominance in their relationship. He's a more chaotic and unpredictable character, and by using this term, he's asserting his own brand of crazy over Spider - Man.
Deadpool became Deadpool through a series of complex and sometimes convoluted events in the comics. He was originally a mercenary named Wade Wilson, who underwent experimental treatments that gave him his unique powers and personality.
There is a loose link. The version of Deadpool in Wolverine Origins provided a starting point, but the standalone Deadpool movies developed his character and story in a more distinct and expanded way, deviating from the initial portrayal to create a more focused and engaging narrative.
It's a bit of a mixed bag. While there's a link, the portrayal of Deadpool in Wolverine Origins doesn't fully align with his later, more developed storyline. Some elements were changed or not fully explored.
One scenario could be during a fight. Deadpool is taunting Spider - Man while they're trading blows, shouting 'baby boy' to throw him off his game. Another might be when they're teamed up and Deadpool is trying to give Spider - Man some unorthodox advice, starting with 'listen here, baby boy'.
Obviously, the main characters are the two Deadpools. They are both versions of the same character but with potentially different backstories and personalities in this graphic novel.