CLEAN : Underwater 'explosions' recorded prior to Nord Stream leaks: seismic institute

The video discusses observed explosions near the North Stream pipeline, believed to be man-made due to the energy released and short duration. The source is uncertain, but natural causes are unlikely. The analysis focuses on the characteristics of the explosions, differentiating them from natural collapses.

What factors make the source of the explosions difficult to speculate about?

Why is it believed that the explosions are man-made?