From the article, he did sneak off the ship routinely after it ran aground some years later. He would sneak off, buy food and recharge his phone, then return to the ship for some bizarre reason.
It is a sad state of affairs, whichever way you look at it.
There's something odd about this story because neither a passport nor money should have kept him there, unless there was literally some kind of watch for him, and/or the cash situation was really that extremely dire. That said, he was able to survive for 4 years so money had to be coming from somewhere.
I suggest that he was maybe being paid a tiny amount, and that he felt it'd be better to 'stick it out' as a nearly worthless cog, than to take a risky path home to what might be nothing anyhow.