Nobody ever said this was anything other than the result of one poll.
And you're right, the way "sophisticated pollsters" calculate things is by the "garbage-in, garbage-out" model. They crank in a bunch of trash polls, along with some better ones, and then claim that because the result is an aggregate of a bunch of trash, mediocre, and good polls, that you magically get a good and accurate result, instead of just garbage.
Nobody ever said this was anything other than the result of one poll.
And you're right, the way "sophisticated pollsters" calculate things is by the "garbage-in, garbage-out" model. They crank in a bunch of trash polls, along with some better ones, and then claim that because the result is an aggregate of a bunch of trash, mediocre, and good polls, that you magically get a good and accurate result, instead of just garbage.