Only if there is nothing between the shooter and the target character. And the game doesn’t actually care what the target is - it can be a character or an object (glass, wall, explosive barrel, etc.), so it only makes sense to speak of to hit chances in the very specific context of targeting characters. And in the game you often shoot at enemies behind walls, glass or other obstacles, or enemies you can’t even see yet, i.e. you are not actually targeting any characters as far as the game is concerned.
It’s not rolling any dice yet. It says “your aiming reticle is covering body parts of the target covered in x, x+10, x+30 armor, and your weapon does y damage, thus the possible damage is between y - x and y - x - 30”. And if 100% of the target is covered by the reticle and y - x - 30 > HPs of the target it shows the skull and crossbones. No dice are rolled just yet. It’s the difference between rolling a dice and saying if you roll a 6 this is what’s going to happen. That’s why only if you see the flashing skull and crossbones you know for sure that the target will be killed.
The thing is, it’s the only practical way to ask the question. Because the bullet (and with burst weapons, each bullet) has equal chances of landing anywhere within the circle, the only way to put this in a % would be for each position of the reticle to say (based on its coverage) you have % to hit head, % to hit arm, % to hit torso, etc. % to miss the target.
You can’t just have the question/answer “what are my chances of hitting the target in the head? 75%? OK, I take that shot”, because you can have the same chance of 75% to hit the head in many different positions of the reticle, and depending on each position the chances to hit other body parts of the target, or missing it also change.