Even your link confirms that the population is in decline, just not as quicky as some reporters say.
"While the fertility rate declined from 4.32 in 1949 to a low of 1.26 in 2005, the total population was increasing >>until 2011<< "
"Japan’s Population Decline Not as Rapid as Media Portrays".
I just noticed I could replace 2017 with 2019 in the official statistics link and did so, resulting in http://www.stat.go.jp/english/data/handbook/pdf/2019all.pdf
It is the same Table 2.2 That still shows a decline and projected decline.
I am not seeing anything that backs up your assertion that
> birthrate of Japan is considered low, but they are growing still
If you still want to assert this as fact then you are going to have to provide a reason that the Japanese government's own statistics and projections over at least the last 5 or so years are incorrect and what should be used as authoritative data instead.