I agree that simply calling something “interest” doesn’t magically make it a regulated financial product. My disagreement is with the idea that “can’t be redeemed for cash” is the dispositive test. Regulators generally look at the substance of the arrangement, not just the label.
Also, your £1,000 credit example isn’t really analogous to the original post. If you simply gift me £1,000 of service credits, that’s very different from me prepaying £1,000 of my own money and you then paying me a return based on how long that prepaid balance sits with you.
The original discussion wasn’t “are loyalty points regulated?” It was “why would paying a return on prepaid customer balances create more regulatory work in the EU?” To me, the answer “because regulators care about products that start looking financially deposit-like” seems entirely plausible.