Is this the same as “inverse contracts” on some CEXs?

No. Many CEX “inverse contracts” (e.g., BTC‑margined BTCUSD perps) are inverse in margin (you post BTC and your position size is quoted in USD), but the index is still the spot price.

HIP‑3 inverse perps are inverse in the index itself: the underlying reference asset is 1/P, while margin is still in stablecoins.