I was once at a tech conference for high schoolers in London where one of the distinguished speakers (others included Vint Cerf, and a UK government minister) told us that the primary reason the sun is hot was because it was still glowing with heat from the pressure of gravitational collapse.

I think their claim was that the nuclear reactions in the sun contributed to the Sun’s radiation, but did not contribute to the bulk of the Sun’s temperature (heat?)

I’m a little fuzzy, but I’ve never seen this claim elsewhere. Is it true?