The article is extremely vague on how they did this. The one big red flag though is that the protocol for the messenger in the article was a bespoke secret design by a single person who wasn't a cryptographer and not a well vetted public one.

I would love to see a technical analysis of the supposed end-to-end encryption methodology used here.

Same here, and would love to find out if they paid the "Million dollar hack" to the Europol people who cracked it!