It'd be more accurate to make claims compared to the smartwatches listed in the study, than claiming it's the most accurate on the market.

> Participants wore an Apple Watch on one wrist, and a comparative wrist-based device on the other, while using a Polar H10 ECG based chest strap as reference. Wrist assignment was randomized such that Apple Watch was worn on the dominant hand approximately 50% of the time. Wrist-based devices studied included Apple Watch Series 12, Garmin Forerunner 970, Google Pixel Watch 4, Huawei Watch 5, Samsung Galaxy Watch 8, and WHOOP 5. Oura Ring 5 was also worn on an index finger, per the manufacturer's stated best practices3

source, via the footnote: https://www.apple.com/HRAccuracy/