As one of the readers to the Aquinas Lesson pointed out, one can cheer for one sports team or another without any moral repercussions. So, it would seem strange that Aquinas would say that the natural law pertains to all human actions.
Further explanation is necessary.
To use yesterday's example, one might not ask another why he danced to encourage a child to smile for a picture. However, this action might take on moral implications if the individual was specifically told not to, perhaps by a parent. At that point, it is legitimate to ask why.