Knowing zero else, simplest answer seems the most logical. It got inadvertently bent while outside of the pistol. It should have been replaced but Bubba the Bender tried and said "huh still works!" and here it is.
Probability dictates that invoking "Occam's Razor" is most often the correct assumption.
But let's dig a little deeper, shall we?
Bubba decides to clean his pistol.
Like most "experts", he expels a half of can of the latest, aerosol "gun goo" (touted by other "experts" on the internet) all over the outside of the gun, his hands, clothes, his wife's kitchen, and every other place it shouldn't be.
Advised by a "friend who knows everything about guns" to field strip it before cleaning, Bubba manages to get it apart, whereupon he expels the remainder of the can to the same places as before.
Satisfied with himself, he endeavors to reassemble his pistol.
He places the guide rod and spring in the dustcover, and tries mightily to push the slide on to the frame.
The guide rod and spring jams against the inside of the spring tunnel and the slide refuses to go all the way on.
This is when Bubba alternately places the muzzle or the beaver tail against a solid object and HAMMERS on the opposite end with a claw hammer from the wife's tool drawer to no avail.
"No wonder!", he exclaims.
"The thieves at S&W sold Brinks a gun with a bent guide rod!"
John