Don't think Belgique was inferring that any fuel dump would be
of "all the fuel". However in the case of a landing on a contaminated runway of marginal length (say), a crew might elect to dump to well below max landing weight. I assume that they could dump down to (for argument's sake) half wing-fuel tanks remaining (for an u/carriage problem for instance).
The question is whether:
a. that would empty the centre-section tank
b. whether the centre-section tank's jettison pumps would run on dry whilst the wing-tank fuel was dumping down to the selected (or preset) level.
c. in which case (a plus b) a hazard might exist from either the electrical shorting or the extreme overheating of the Hydro-Aire pumps.