Yep. Actually on meta level I see more confirmation bias right here. For instance gwern doesn't seek to disprove that it is confirmation bias, but seeks to confirm it, and sees how the print statement after suspect line wouldn't disconfirm the bug being on that line if the bug is above that line, but doesn't see that it would disconfirm the bug if the bug was below suspect line. (and in any case if you want to conclusively show that there is a bug on suspect line, you need to understand what the bug is, precisely, which is confirming evidence, and which requires you to know the state after and see if it matches what you think the bug would produce.)

I do imagine that confirmation bias does exist in programming whenever the programmer did not figure out or learn how to do it right, but learning that there's this bias, and learning how to do it right, are different things entirely. The programmer that learned how to debug can keep track of set of places where the bug could be, update it correctly, and seek effective ways to narrow that down.