Totally unrelated. I guess there's a chance that the service might have been built using the Matrix protocol, but we're unaware of it if so - and the app in question doesn't look like any Matrix client I recognise. Unfortunately this looks to be a particularly unfortunate namespace collision.
Grateful to NL Times who included this line in their article: "The investigation did not spotlight the similarly-named Matrix open source communication protocol." https://nltimes.nl/2024/12/03/dutch-french-police-take-matri...
Of course, we are staying tuned as more information becomes available.