No the estimate comes from the theory
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Proves my point - its a theory and a statistical conclusion. No facts need apply.
Maxwell's equations, and General Relativity are theories, supported by statistical inference from countless experiments and experience. The inferences about the number of interstellar objects is much weaker, but not ridiculous. Until we have more evidence, and with the more sensitive sensors that should be available in the near future we will. In the meantime, we should to keep an open mind, agreed.
Heliocentricism, too, is "just" a theory.