It's one of those things where it's technically correct but the headline is misleading. When you say "a triangle" without any qualification as the headline does, people are going to interpret that as a good old fashioned triangle. Using the term without clarification that you mean spherical geometry is kind of underhanded writing, imo.
It's a mild form of clickbait.
I think it's just a normal ages-old pattern for writing headlines that pique people's curiosity. It's super common in popular math in particular, because math is always about generalizing. There's a fine line between that and actual clickbait meant to actively mislead.
The title attribute of the article is <title>A hyperbolic triangle with three cusps</title>