Remember MW1's Ending?

I guess it was a finished map but not fit in the storyline so ended up as bonus mission.
Player is part of the Task Force 141 like later in MW2.

It didn't seem related, just another "secret mission" the squad went on.

my guess is that it was meant to be a mission, but since you could finish it in a matter of minutes they decided to keep it as a bonus mission, also it served as an experiment wether people liked them or not, which lead to special ops.

so no, its not related at all to the main storyline, ir any storyline in call of duty whatsoever