When stocks fall hard, investors usually buy government bonds and central banks cut rates. Both push long bond prices up. That's why long Treasuries have tended to rise in exactly the weeks a leveraged equity position is falling, and why the signal holds TLT while its gates are shut.
Over the full study, holding 20-year Treasuries while out of the market gave 39.5% a year against 35.3% with T-bills. Most of that came from one thing: yields fell from over 10% in 1985 to under 5%, and falling yields mean rising bond prices. Strip that out and keep only the coupon, and the result drops to 36.1%, barely above T-bills. The coupon is the part you can expect to repeat.
The hedge depends on stocks and bonds moving in opposite directions. In 2022 they didn't. Inflation pushed yields up, so bonds fell with stocks. Holding TLT through that bear market returned −32%, close to the index's own −35%. The same thing happened through the inflation of the 1970s.
So TLT is a hedge against crashes caused by falling growth, not by rising inflation. The signal keeps TLT because over the long run it has helped more than it hurt, and the monthly research note will flag it when that trade-off changes.