Horribly guilty drug lords using the proceeds of crime to fight on a piece of evidence on a technicality is what this looks like.
Difficult to see why it would be inadmissible tbh 
Yeah the article seems to imply that using a honeypot to entrap criminals is somehow inadmissible but does not give any details to why it could be.
EDIT:
After a bit of a Googling about the case it looks like the issue is over the extra info gathered when the messages were duplicated.
Additional information, including geolocation data, was also added to the duplicated messages as the users pressed send, but not to the original texts, the court heard on Monday.
Reminds me with the case of the guy known as “Doingfedtime”. USPS broke the law and opened the packages sent by him, so used that to his advantage, Mind that he was actually dedicated to it, and not an easy thing to pull off.