I think that's a very cheap way to make a donation. Because let's not forget that this guy doesn't promise them 1 million perse, he only promised to go as far as 1 million when doubling whatever funds they can get their hands on.
So how likely is it that TNMOC can lay their hands on a million? This seems like damage control to me.
If that guy really wants to do something for this museum then he should simply donate an amount of money which they can then spend instead of using tricks like these.
Still, maybe that's the plan all along; getting geeks a bit worked up so that they'll donate too in order to make sure that he'll have to go all the way with his one million pound.