To be fair, all of that is not necessarily truly inaccuracy on the part of the show writers and/or creators. These things are rampantly portrayed inaccurately in Hollywood, not because they don't know any better, but because to them they think it's cooler to the viewers to see that kind of action.
Also, depending on who was the one pulling back the hammer, and on what weapon, it could have been a fresh magazine, and it's only a single-action handgun? Or perhaps it's still only a single-action handgun, and regardless of new magazine or not, is kept in holster without the hammer pulled back? I don't know, I honestly never pay attention to these details in fiction, because there are many conceits when translating reality to what viewers find entertaining.
Now, if you want to talk inaccuracy on the part of plain stupidity, it's usually military uniforms. Note that the common misconception that military uniforms must not be displayed 100% accurately in media is 100% false. In fact, there are Hollywood production advisers that are ex-military, who make a point to put forth realism in military portrayals when producers utilize their talents. All the sloppy berets, missing patches, etc etc? Either ineptitude, lazy research (which could be grouped with the former), or, perhaps they knew what was real but thought it would be more entertaining to do otherwise.
But the worst offender is anything "cyber." I guess one might think that, sure, computing is, like, hard man, but firearms? Been around for eternity, of course they should have that down pat! But... Hollywood be cray-cray. Entertainment most often trumps realism, for many reasons. Ineptitude may be a reason, but more often than not, I would wager it is a strategic decision.
edit:
Also, I am with you in that I presume that line was meant to point to his effort in creating an excuse. If you've never shot a crossbow, I can't imagine most people would hit their target on the first try. It may be easy (I have no idea, never shot one), but figuring out the true aim on any given weapon usually takes a little bit. Unless you're a seasoned veteran with weapons, then you may understand how the different aiming systems and iron sights work.
Do you have any means of dialing in a sight on a crossbow? I've really only ever shot rifles, an occasional pistol but very rarely. I'm no crack shot, so... I think I'll just shut up now.