back on topic...
It has been a pretty strange day ... Confused about Ellie's sexuality and Ellen page has just come out as gay..coincidence??.. the scene just caught me off guard.. whatever subtle hints there were i was not picking them up..
The kiss was a shock and I am sure ND meant for it to be a shock.
Ellie was probably confused, or did that out of impulse when she realized how much Riley cared for her.
Whatever the case, props to ND for doing it in a meaningful way.