But the watch didn't detect a fall. The watch saw signals and data points and thinks it could be a fall. Saying "Fall detected" is too confident and not a reflection of the feature.

You’re right. Better explain all that to the user of the watch who is laying on the floor.

If they are not laying in the floor then they already know it’s wrong.

"Fall detected. Call 911?"

“Huh? No, I didn’t fall. Don’t call 911”

Or

“I did fall, but I’m fine. Don’t call 911”

Maybe you can explain to the user of the watch who didn't fall but the Watch suddenly says "Fall detected".

Apple's version is better. It's more accurate of what the feature does (guessing based on factors), and it's more human.