yes it is.
are you using your phone and is it working or are you staring at it looking for a wobble?
This is just a modern day version of Hawthorne's The Birth Mark
It's to try and prove or disprove that the phone is extremely flimsy. If it bends slightly in that short of amount of time it doesn't bode well to the integrity of the device. My worry would be the screen coming loose mostly, if you require a functional non cosmetic reason to be concerned.