The statement, "The honor of the family is intact,"indicates that Vincenzo's presence was meant to shame Frankie out of testifying for the government.

BUT: later, when Tom visits Frankie, he likens the old Corleone Family to the Romans and concludes: "... Unless they went home and uh, killed themselves -- then nothing happened. And their families -- their families were taken care of..." Tom replies: "Don't worry about a thing, Frankie Five Angels."

We can infer that Frankie had been threatened--either that his own family in the US would be harmed, or that Vincenzo and his family would be harmed, unless Frankie not only recanted, but killed himself. So, I think both views--honor and threat--apply.