Monkey and Pigeon?

Monkey and Pigeon

Daily Mail

The novelist Victor Lodato writes an interesting article for the NYT of how he became best friends with Austin, a woman in her eighties, when he was in his early forties. Titled "When Your Greatest Romance Is a Friendship" (February 24, 2017), the article implies that their "Modern Love" remains a Platonic one, or "like one of those unlikely animal friendships: a monkey and a pigeon, perhaps" - not sexual, at any rate. Or does it imply this? Let's see:

Austin had [recently] attended a wedding. She showed me a copy of the vows, which had been distributed at the ceremony - a detailed list. I read it carefully, at Austin's bidding . . . .

"I never had anything like that with the men in my life," she said, pointing to the vows. "We loved each other, but we didn't have that." She was crying now, something she rarely did.

I took her hand and said, "Well, you have it with me. Everything but the sex."

At which point, the monkey kissed the pigeon.

That night, I had an odd realization: Some of the greatest romances of my life have been friendships. And these friendships have been, in many ways, more mysterious than erotic love: more subtle, less selfish, more attuned to kindness.

That's what Lodato writes, but what does the expression mean, "the monkey kissed the pigeon"? Is it merely something like "the groom kissed the bride"? Or more toward what that kiss is intended to lead to? And is there some weird idiomatic meaning here that I happen not to know?