Seemingly logical, but ignorant and likely incorrect.

Leaking is any unintended oozing, sweating, transfer of tank contents to outside tank.

With increased temperature and pressure, gauges red lining, etc. it's very probable there's been leakage and / or venting.

The creation of dikes and dams to contain greater spillage from a potential low level rupture is in anticipation of more than just a leak and ideally less than a full thermal run away and explosion.