[whatok]

If I were to hear interest rate mentioned in relation to a bond, I would assume they were talking about the coupon which in this case is fixed. I think you have the right understanding, various yield methods basically are just the IRR of the security under different assumptions. If you bought at par and held to maturity, the yield would be equal to the coupon which in this case is 5.3%. Without knowing where the bond is actually trading, given that it has a yield higher than its coupon, you know that it is trading below par; the difference is how much it is trading below par under the assumption you get 100% of the principal at maturity.

I wouldn't normally refer to the return as "fixed" as that is primarily only used in reference to the coupon and because of the fact that you mentioned earlier in that sentence; bonds fluctuate in price so the yield is regularly changing given a change in price.