Actual interrogations are far more cunning and complex, involving psychological tricks and play against weaknesses in the human mind. Perpetuating this "they'll hit you until you confess" bullshit stops people from learning actually useful information about how to resist interrogations.
Pedantism and comics do not go well together. The format is not meant for conveying exactingly precise information. Interpretation is required.
This sort of interrogation typically starts with "we know you did it, so why don't you make things easy for yourself...", not "break his finger so he knows we're serious".
The XKCD 538 fallacy is the delusional belief that torture and threats of violence are how people are coerced into confession during an interrogation. That is not the case. Perpetuating that fallacy actually helps interrogators, since the fear of "confess or else you'll get the wrench" is implanted in people's minds. Since that is not how things actually work, it is counter productive. It does not help anyone except the authorities. This is why I say stop perpetuating the fallacy. Seriously.
Seriously, you are not telling anybody here anything they did not already know.
There are many creative ways to circumvent encryption, and one of those ways could be something sinister like a wrench-torture, but it could also be through social engineering or psychological craft. The wrench is just an extreme example, maybe even a metaphor.