Actually tested myself and got very surprising results.
The defending ship had a self destruct device and my boarding ship captured it. So apparently the self destruct didnt go off after it was captured period and neither ship was destroyed.
I'd say self destruct is broken or not completely working. Neither ship had weapons so component was damaged
ran it 3 times seemed to be same results. The self destruct i believe is tied to the button in the simulation key pad and may as of now be the only way to destroy a ship. Doesnt seem like if it is a problem would be hard to fix. But as of now self destruct seems useless for most practical uses