Well, that is self plagiarism. Although I don't agree with the question or how that was handled, it is using your previous work without citing that you had previously written it.
An interview has to show capability, self plagiarism is not relevant there.
Anything can be considered relevant in an interview -- excepting illegal discrimination.
I guess the corollary would be a baker asking a potential apprentice to bake a baguette and send a photograph. Sending a photo from your blog of a baguette you cooked a year ago might still be considered disingenuous, even if it shows capability.
Well, no, because a code snippet is the same every time you write it, whereas an apprentice may, even while following the same recipe, produce variations in the result due to the nature of baking.
If you can write the exact same (non-trivial) code twice, that's fairly remarkable.
Alas they'll attempt to justify it by saying they want your capability now, not X years ago. Maybe it's not entirely unjustified -- I have some old mathematical code on github that I don't think I could explain the technical details of without many hours of review, I wouldn't want to be hired to produce more code of that sort without an understanding that ramp up will be needed to return to my previous level. Given something like quicksort, though, I'd just get the feeling of "dance, monkey, dance".