He says that: “for most short positions you earn income”
You receive the financing rate when you short an index (so you sell it above the index price)
On something like tesla your short borrow costs are generally above the cost of financing so you don’t get paid, but in the index space you def do. Particularly if you’re willing to lend Russell 2k index the short financing you’ll be getting is usually 15-30bps over 3m libor
Disclaimer: Consult your financial professional before making any investment decision.