It's difficult to never mention something so important, even if it's a local department rule. And once something like stingrays are well known to the public then it can be a fair inference that they are used in cases where that is the simplest explanation for how the police found or tracked a suspect. Poor OPSEC on the part of the police is basically a given in a society where we have public trials and due process (including discovery).
Whether the law allows or should allow the use of such devices, and whether with or without a warrant is up for debate, but it can't allow hiding their use, not in an open society with due process. It was always bound to be the case that some judge would think so, that some police note would leak this, that some police office would testify about it, that a Snowden would leak it, or that the public would figure it out anyways (especially when it comes to active devices).
So I wouldn't blame bad OPSEC on the part of the police here for anything. (Not that you are. Just saying.)
The defendant in the story, BTW, is not very sympathetic. In general, for test cases, one wants a sympathetic defendant. That's because judges are at least somewhat biased, typically. A judge has to imagine a much more sympathetic defendant and set of circumstances in order to convince themselves to continue with a line of argument that leads to the defendant being cleared on a technicality.