The screen shot isn't going to tell you anything. Those can be hacked to say whatever.
The phone isn't stock if its been rooted. The phone can never be truly returned to stock once its rooted. The bootloader has been unlocked (which HTC has a record of) unless the user happened to make firewater temp root work, and s-off without unlocking the bootloader, which I think is very unlikely.
A screenshot of the bootloader screen would be more useful, as it would tell you s-off or s-on, if the bootloader is locked, unlocked, relocked, and other details which are harder to change than within the OS.
Even then, if the bootloader says s-on, you would never know if the previous owner did s-off then returned to s-on, which still throws a security flag that can't be changed.
Or are you asking if its been returned to stock? Any phone can easily be returned to stock, now that the AT&T RUU is available.
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Phone: AT&T HTC One (M8)
Tablet: Samsung Galaxy Tab Pro 8.4 (WiFi only)