For example if Tanaka's salary is $500 lower because the company is partially paying for their place, that means on paper his salary is lower, the price of the place is MUCH lower, and the ratio of housing/salary is also lower, than if he received those $500 and then used it to pay for the house.
e.g. https://www.gtalent.jp/blog/japanwork-en/social-insurance-we... or https://www.reddit.com/r/japanlife/comments/54fjgf/how_much_...
I know 3 Japanese people (nothing to do with foreigners or foreign companies) that had their house paid by the company totally or partially, and they told me it was common in their company/industry. And those were large industries (train company, hospital, manufacturing).
Mine is anecdotal, but from how they described it it's an anecdote involving hundreds to thousands of people indirectly, so I'm very confident that it's not an isolated thing.
50sqm is a large apartment for a single person. Without checking, I’d guess somewhere in the neighborhood of 20 man per month.
A part time janitor would gross half that.
I don't think it's extremely common to live in actual employer provided housing.