The layout requirements doc describes the use of non-cursive fonts for book and article titles, etc. This would correspond to a similar practice in Adlam, for which a Noto Unjoined font exists.

There is no equivalent Noto font for N'Ko, although the usage in Solo Farabado Cisse's book and in https://cormand.huma-num.fr/maninkabiblio/periodiques/silabosoona5.pdf seems to point to this being more than just a legacy font bug.

Can anyone confirm that this is indeed an intentionally different font/writing style that is in regular use?