What the first article states is:
5G NR (New Radio) does not cover low power wide area network (LPWAN) Internet of Things (IoT) use cases in the current 5G release.
There are many use cases for 5G, and 5G NR being relatively new, has focused at first on other use cases. The same could be said for LTE and LTE-Advanced, which at first focused on broadband mobile data services and handling them well. Later only, it added specialized support for IoT in the form of technologies like LTE-M and NB-IoT. In the same sentence that the article says NB-IoT is not a 5G technology, it also says mentions 3GPP Release 13 and 14, when NB-IoT was introduced. Note that LTE itself was introduced with 3GPP Release 8 earlier on.
4G NB-IoT (Cat NB1 3GPP Release 13 and Cat NB2 3GPP Rel14) is actually not a 5G radio technology.
Your second link just describes frequency bands and allocations for 5G. It doesn't mean that 5G and 4G bands are mutually exclusive. 5G bands are more of a super-set of what was available for 4G.
Hence, LTE-M and NB-IoT are definitely 4G technologies.