Difference is timescale. Coal “sequestered carbon” over millions of years, and released over a few decades.

Biomass gathers and realeases on the same timescale

From the article:

In a statement, the police in Finland said the authorities had boarded the Eagle S tanker in Finnish waters.

So no international waters in this case. In fact there are no international waters in the Baltic Sea ( https://en.m.wikipedia.org/wiki/International_waters )