Does this kissing have anything to do with sexuality, though?

imo... yes, obviously im not taking a peck on the cheek here, it doesn't nessecerily mean they are lesbians but (in the words of the article)

“It may be that girls feel their way forward without identifying themselves as either homo- or heterosexual,” said Rembeck.

She thinks that girls are also more inclined to experiment than boys.

“There is less of a taboo for girls. During their teenage years girls are often a bit more intimate with each other in their own way.

So yes would be my answer...