I can't find the documents/video but you can see that the self destruct explosives do indeed go off.

All that they do in starship is punch holes into the fuel tanks. Then, as soon as air mixes with the fuel in the correct ratio, boom.

However, there was too much pressure in the fuel system and it was jetting out so strongly that it appeared O2 wasn't mixing with the fuel.

After about 10 seconds you then see it explode.