Well, it is clear that the understanding of Japan's government regarding working with a tourist visa is different than that and that it indeed didn't allow working even if remotely for an overseas company.
Otherwise, they wouldn't hassle themselves to introduce a new kind of Visa that is geared towards exactly this kind of situation.
A digital nomad visa serves an important purpose: it allows someone to stay in the country longer than as a tourist. The existence of a digital nomad visa bolsters the understanding that digital nomads are allowed to use a tourist visa.
A working visa is very difficult to get in most countries and requires local sponsorship because of the risk to the local economy — you’re potentially taking a local job from local people. Tourist visas are easy to get because there’s no risk: a tourist arrives, spends money, leaves. A digital nomad is a tourist by every measure.
The reason tourist visas are short is to ensure people don’t move to the country without permission. A digital nomad doesn’t present a risk to the local economy so bumping their length of stay is safe for the local economy, hence, digital nomad visas.
Otherwise, they wouldn't hassle themselves to introduce a new kind of Visa that is geared towards exactly this kind of situation.