East can't beat 6 spades and the double would cost a little. Still, even looking at 7 clubs, East can't presuppose that dummy will have nary a one, and I think the Lightner double, with that reasonable chance that it will beat a big contract, was within the ballpark. And his partner should have honored it. East bid clubs and then doubled. So any interpretation of the Lightner double calls for a diamond lead.
The double (with a diamond lead) gives up about 4 IMP's over simply letting it go. But had that been the deciding lead, that would have been worth 15 or so IMP's, not a bad gamble, I would say. This is not the same as doubling a little slam with no strong expectation of a second trick. In such a situation, you're far likelier to be pumping up declarer's score than not.