I have to admit that I didn’t follow LMDE closely, but to my knowledge there have been some changes how it updates. Also in your provided link it says:
There are no point releases in LMDE 2, except for bug fixes and security fixes base packages stay the same, but Mint and desktop components are updated continuously.
which I would interpret that only the Mint features are updated on a rolling base whereas the system itself is not. As I understood the concept of LMDE there will be occasional major releases with a new base system, whereas the features and software only are updated on a rolling base.
Nonetheless, I also find it an interesting option, as out of the numerous Debian and Ubuntu derivatives, Mint was amongst my favorites (of the ones I tested).