The bomb was actually too large for a controlled explosion, with 2,400 kg of explosive, so instead the navy divers used a technique that was supposed to cut open the casing and burn the explosives inside. This was the successful result

Ah; cutting charge forced a sheet of molten metal through the middle of the thing? Or---charge forcing a slug of water into the middle of bomb to disrupt it?

That's all the details I had. Since it was supposed to burn I assume something like the former only multiple cuts. Obviously success was defined as no casualties and no property damage rather than no explosion.

The Polish MOD described it as deflagration and said: The object can be considered neutralised, it will not pose any more threat to the Szczecin-Swinoujscie shipping channel. https://twitter.com/Poland_MOD/status/1316282610071592960

If you look at this video covering the original attack, starting at around the 52s mark there is an explosion free splash which is probably this device https://youtu.be/vt4iqwkTJkQ