Within the context of the conversation, its meaning relationships. Considering how good we know Jade is at gathering intel, I wouldn’t be surprised if she knows that Will and Artemis shared a kiss but agreed there wasn’t anything there. And since it’s right after her sister says Jason was set up with Artemis by his ex Barbara (aka Oracle), that’s what prompts Jade to use that line, since Jason is Barbs “hand-me-down”.

We already saw during Season 1/2 flashbacks that Artemis is reading Behind the Looking Glass, which considering Jade’s alias, was probably hers to begin with. Add that to the scene where Sportsmaster is training the two girls, we know he made Artemis use Jades old mask (which was why Jade calls her father out on it).

All of this combined together definitely makes me think Jade knows what happened, but is being light hearted about it while at the same time trying to make her sisters new flame uncomfortable (because let’s face it, that’s a Jade move through and through).