More revealing: The same passage said that, because Tess didn't live at the Mall, some outsiders were unaware that he was under Vito, which Vito wanted because it made his foes underestimate him.

That leads to an ancillary point: the novel several times says Vito had a policy of making people underestimate him. The upside would be that they'd get careless around him. But, the (unstated) downside would be that they'd be emboldened to make moves on him, whereas if they knew his real strength, maybe they wouldn't try.