Inaccurate step count in Health app on iPhone

Why is apple iPhone health app is giving wrong data?

I did brisk walking of 16,412 steps yesterday. I determined to beat my own record by staying longer than that of yesterday.

when I got home after 2 hours, checked my health app, it showed 9,507 steps!

I feel cheated! I noticed same in the past, told 2-3 people about it but they thought that I was probably wrong. Is there any reason and solution for this?

apple often believe that they can never get it wrong or make mistakes! Would Apple takes responsibility for this time???

[Re-Titled by Moderator]

Original Title: Health app