"On his [Mr Knightley's]side, there had been a long-standing jealousy, old as the arrival, or even the expectation, of Frank Churchill. He had been in love with Emma, and jealous of Frank Churchill, from about the same period, one sentiment having probably enlightened him as to the other."

So I would say that yes, the two lovers are just having a bit of light-hearted fun in Ch. 53. Mr Knightley has always liked Emma (remember this from Ch. 5: "I have a very sincere interest in Emma. Isabella does not seem more my sister; has never excited a greater interest; perhaps hardly so great. There is an anxiety, a curiosity in what one feels for Emma. I wonder what will become of her!") and over time his affection for her turned into more than just friendship, but he didn't realise this until Frank Churchill was talked of. Emma has always been an "object of interest" to him, but the "daydreaming of a future match" is a relatively new habit of his:D