Space

To clarify, that's the collision of 2 dark matter particles.
Not the collision of a dark matter particle and something else.

researchers report that they have detected the invisible scaffolding based on gamma rays that result from the collision and resulting annihilation of two dark matter particles.

So, that's 2 particles of this unobservable (or, difficult to observe) matter interacting with eachother in an observable way.
Very cool

I have to agree :)

but then they would be decent

Lmao, what? No, if they put "indirectly" in the headline, then they'd be just as decent but actively wrong about it being the first time. We've detected dark matter in plenty of indirect ways, from the Bullet Cluster to the angular velocity of galaxies. I don't think you understand how often particle physicists observe things based on predicted properties (such as "this decays into that") rather than something we see "directly".

Dark matter is dark matter because it only interacts gravitationally with "normal" matter and energy, and we've already observed that gravitational interaction. So what's your standard for not qualifying a dark matter observation as "indirect"? Did you want two dark matter black holes colliding? Did you want the scientists to magically change how electromagnetism works?

It's fine if you don't think this is an observation of dark matter at all, but "indirect" is needlessly splitting hairs in this field. You can read the journal article – at least the abstract – and see what the evidence is.

In the field this is actually refered to as direct observation. It's confusing for someone not familiar with the jargon as it is very similar to direct detection.