Doesn't Tokyo have very low unemployment? According to Wikipedia: Japan 2.5%, Singapore 3.2%, USA 4.1%, EU 5.2%.

I expect Tokyo is probably even lower than the national average. Visiting just as a tourist it seems like Japan is quite good at creating, I don't want to say bullshit jobs, but perhaps not-that-necessary jobs? Jobs which mainly serve to give something to do to (usually) elderly. My understanding was that the idea is to make them feel to be a contributing part of the society(?)

I mean all the people controlling the pedestrians or acting like "human signs" and such.

Am I getting it wrong?

Don't make the mistake to think these jobs are just there to keep bored retirees active. The basic old age pension (kokumin nenkin - for sole-proprietors and people who have worked in non-permanent positions or small companies) is significantly below the poverty line at 70,600¥ per month -- that's $450 and that's if you've worked for 40 years without any gaps.

The vast majority of old people working these jobs, e.g. construction site security, do so because they would likely starve without it.

Due to its aging population and lack of mass immigration, Japan has a desperate labor shortage in many fields.

I don't think taxi driving in Tokyo is one of them (because, as noted, the qualifications needed are pretty minimal), although eg bus drivers are in extremely short supply.