Why Do the My Dad Wrote a Porno Hosts Say Oral Sex Is No Substitute for Protein or Salt?

In Belinda Blinked, after Belinda Blumenthal finishes oral sex with Peter Rouse, the book says she adored the salt and that it saved her from eating too many high-protein peanuts. On My Dad Wrote a Porno, Jamie, Alice, and James read that line and reject it.

They say semen is no substitute for protein or salt, joke that a dietitian would not sign off, and decide Belinda has mistaken a penis for a peanut. Belinda even smiles at the thought, which arrives while her mind should have been on Peter. He notices, asks what she is smiling about, and she tells him it was about salt.