If their mumbo jumbo give stable result (let's say "creating force field around spaceships" - psionic shields shown in stream) - it's technologizing. Technology is highly predating sicentific method or actual understanding - first people who used seafaring actually hadn't any clue about Archimed law or how it's works, they just noticed wooden rafts don't sink, as a rule.
There is countless (literally) things that can happen when psychic POP tries, for example, to read somebody's mind, so there are two possibilities:
1. They tries to read a mind and it's works. Why? Another question, but if it happens stable, the very first sentence in this point is a description of technology.
2. They tries to read a mind and SOMETHING happens. Mind has been read. A head of psychic exploded. A head of victim exploded. Some star dims. Planet became marshmallow. All of this in same time.
Even Warhammer psy is technologized (and humans don't know HOW it works) to the extent it can stable used in war.
The very idea behind propaganda or advertisements is that human behaiviour in every culture HAS stable rules (known or not-known). You can actually predict how will people act and manipulate them.
There's a big difference between observing the limits and abilities of psychic powers and figuring out how they work or how to replicate them. The effects might be reproducible, but if the only people who get psychic powers are those of a certain ideological leaning with a relationship to the god-like entities who bestow those powers it's vastly more difficult to study and reverse-engineer.
It's not like psychic powers in stellaris are some sort of purely natural, evolved trait. You can't point to a part of a psychic pop's brain and say "there's the Organic Subspace Sensor Neural Network that allows for mind reading!" It's very literally the realm of "aliens" vastly more powerful.
And sure, perhaps eventually materialists with enough time and resources could figure out the basic physical laws and replicate the effects. But that assumes the Shroud beings will let them. Given that there is an eldritch/40k theme to the psionics of stellaris the researchers might fail for reasons ranging from none of them agreeing on what they've just observed (with digital recordings being equally vague) to all going completely mad.
There are a few things in stellaris already that are nods towards lovecraft. As much as the tentacled, elder alien race trope is slapped on everything these days the key theme of Lovecraft's work was that knowledge existed beyond human experience that was inherently destructive to the human experience. A huge part of why Lovecraft is so effective in the modern age is because it's the antithesis of the post-enlightenment belief that knowledge is power and one can learn more about the universe without risk beyond the trivial (i.e. the mundane safety concerns of a lab). In a Lovecraftian world learning new things is as risky as ingesting strange new plants. Could be nutritious, could also poison you.