The public doesn't have the right to know, since no law was broken. The engineer was identified by a "former state investigator [who] spoke on the condition that he not be identified because he was not authorized to speak."
Yes we do, it's in the second paragraph of the article.
"The F.C.C. recently closed its 17-month inquiry into the project, Street View, with a finding that Google broke no laws but had obstructed its investigation."
Even if we didn't, that's also a reason for not disclosing this person's identity: innocent until proven guilty.
Well, usually, the individual who comes into possession of the information decides whether it should be public, using their own sense of ethics. And questions like "how does this benefit the public good?" are precisely the kind of thing used as input to that ethical calculation.
The public has the right to know. Otherwise, who decides what should be public or not, the ministry of big brother?