He's right. I misused the terms. "Interest rate" isn't precise at all, and since we're talking finances, the details are actually important and I should have been more careful about which terms I used.

There is a "coupon", which is the amount a bond pays each year. Which is one kind of interest rate.

There is the "yield to maturity", and since Tesla's 2025 bond seems like a normal bond, so Yield implies yield-to-maturity. This is another "interest rate" but just saying "interest rate" is meaningless.

Since coupon vs yield is ambiguous, I should have used more precise language earlier.

> bonds fluxuate in value but the return on the bond itself is fixed, so the yield reflects the relationship between cost and payout

Yes.