Yeah after reading the FAQ I came to the same conclusion. But also realized that pirates wouldn't actually need this site and could just get their own AIS receiver's
Those are mostly oil tankers. Since 20% of the world's oil passes through the Strait of Hormuz [1], the Iranians threat of closing that passage has petroleum prices recently. More analysis at The Oil Drum [2].
edit. Ahh never mind they don't seem to have any data on the east coast of Africa