If it's significant then what's wrong with using a scale that reflects that, even if the numbers are small in absolute terms?

In this case at least, they're going from a peak of ~1.66 posts/day to a valley of ~1.54. As an aggregate that looks like a compelling pattern, but consider it on an individual level: we're talking about one post every ten days. Initially looking at the graph made me think the difference was way greater than a post every ten days, so I'd agree with the GP that it is misleading; I was mislead.

Yeah, but if one post every ten days really is predictive, then showing it at a larger scale isn't helpful.

Looking at the graph, it seems like we're talking about ~16.5 posts in the ten days before a relationship versions versus ~15.7 in the ten days after. In the context of an individual, Facebook might be able to combine this with a bunch of other data to make guesses about people entering relationships, but a quick look at the graph makes it look like they could do it from just this one piece of data.

FWIW, I think people are often too quick to dismiss graphs as misleading due to the y-scale and I do think the graph is interesting. That said, I think a lot depends on the context, and being directly below "When You [emphasis added] Fall in Love, This Is What Facebook Sees" makes this seem misleading.

this is such a classic way.

"Fake news" seems to mean different things to different people. What do you mean by it? That it's not important? That it's just entertainment? That it's false? That it's propaganda? That the person posting it here is doing so for some nefarious reason? Something else?

I would say he uses it like everyone else - for any news/source they don't agree with.