I agree with you that expecting a poet to be both creator and interpreter is
expecting that person to participate in two roles.
Poets, however, routinely participate in both roles. Eliot wrote
extensively upon the poetry of others and as Nancy pointed out provided his
own readings to his poetry. TWL, according to Eliot, is but a collection of
rhythmical grumblings (I paraphrase). Yet he also apparently thought it to
be major poetry indeed.
I think the problem comes with someone's expectations concerning a poet's
readings. The poet cannot be expected to produce a definitive and
uncontestable meaning to his/her poetry. The student in the "three white
leopards" case seems to have been expecting just that. A friendly observer
might find Eliot's response the only fair response possible to that
perceived expectation. An unfriendly observer might find it arrogantly
flippant. Again we have numerous seperate "meanings" and receptions to a
poet's phrasings none of which are definitive beyond contestability.