There were actually two Polish train hacking debacles, and I'm not 100% sure which one the GP means.
The one you describe is the more famous one, but there was another one a few months earlier, where a group of actually malicious hackers used simple radio signals to trigger emergency stops on dozens of trains over the course of a few days.[1]
"Saboteurs" suggests it's the third-party-repair-prevention case. Stopping trains by playing the right tones on analog unencrypted radio (with the tones and frequencies being public knowledge) is hardly hacking anyway.
The one you describe is the more famous one, but there was another one a few months earlier, where a group of actually malicious hackers used simple radio signals to trigger emergency stops on dozens of trains over the course of a few days.[1]
[1] https://www.wired.com/story/poland-train-radio-stop-attack/