They were on a different radio channel than the distress call
There is a particular frequency that distress calls go out on, you are required by maritime law to always be tuned into that channel. So to claim that you are innocent because you weren't tuned to the channel is like claiming that police didn't respond to a 999 call because the operator was using the line to talk to their friends. They are still basically admitting to breaking the law.
By the time they switched to the same radio channel, another vessel was already helping
Should they were not tuned into a illegally mandated frequency for a good while then. They still have questions to answer.
The fact that the vessel wasn't in immediate danger is irrelevant because they had no way to know that because they weren't listening to the distress frequency.