Fauci is correct, partly. Gain of function has a vert specific meaning in cell biology. But it's like calling someone out for mispronouncing a word.
Perfectly clear what Rand meant, and Fauci couldn't resist 1 Being 'right' in a narrow technical sense 2) Taking the opportunity to deal scorn. They like to crow dunghill roosters.
No different from ours shills in that.