It's tricky to evaluate what this rating means for RIZIN because they had things working for and against them;
On the helping side, Fuji supported them by having Tenshin on a very popular variety show as a direct lead in to the RIZIN broadcast, which in turn started off immediately with Tenshin's entrance, which should definitely have helped ratings.
However, the RIZIN broadcast had to compete with a hugely popular show on a rival network that targets the same demographic as RIZIN, which should definitely have hurt their ratings.
Overall, I guess you could classify the rating as middling, good but not great, solid. Which has been a trend for RIZIN over the past shows: They have consolidated their audience and show no signs of falling off, but they are not taking off either. They are incrementally inching forward. They have managed to be much more cost efficient however, as they can now draw the same ratings using their own talent without having to shell out the big bucks for name fighters.