An iso file containing its MD5 hash?
With a secure hash function what you are describing is entirely impossible. MD5 is considered totally broken and yet I am unaware of a method of accomplishing this feat even with known multi collision attacks.
SEJPM gave a relevant link to what can be done with multi collision attacks on MD5 but placing the resulting hash in plain text is harder and I don't believe has been done. Definitely didn't happen as a matter of fact implementation detail. Should someone do this even with MD5 it would be a significant cryptography feat.
In order to demonstrate that with a turing complete format it is easy to have a file produce its own hash with no need for cryptanalysis: I created a proof of concept and wrote a Scala program which prints its own SHA-256 hash. This technique can work with any hash function, and any turing complete language, including postscript
https://gist.githubusercontent.com/meirmaor/3d858568d5da35f568fe96687ed7dbaf/raw/c26d3bdd298567e76e92c6c37ab96e353a3d8cdf/QuineHash.scala

scalac QuineHash.scala
scala QuineHash
6bae798a607d1f74630734435cc93d17c9b92a6705f7663c6fd47f7439c69669
sha256sum QuineHash.scala
6bae798a607d1f74630734435cc93d17c9b92a6705f7663c6fd47f7439c69669 QuineHash.scala