Board Thread:Boruto: Naruto the Movie/@comment-26010916-20150806143152/@comment-24949460-20150811174834

Actionmanrandell wrote: I believe that she has been secretly practicing it i don't believe that was her first use of it.

notice how she states LOCK ON this implies it was a technique she had used before maybe she got a hold of some gentle fist scroll after awakening it

mind you there is no proof that this was her first time ever using the byakugan Well to Naruto and Boruto we know that they never known Hima to awaken the Byakugan. Even Hinata doesn't know about this.