Of course, I would assume telling someone of their legal rights (“you don’t have to testify, you are entitled invoke the fifth”) is a lot different than telling them “you shouldn’t testify” when there is no fifth involved for the witness. Although telling someone to invoke the fifth might be interpreted as an admission of collective guilt, depending on the circumstances. The judge and jury cannot consider it when a person pleads the fifth instead of answeing questions, but evidence of people telling each other “plead the fifth” I would assume(?) is direct evidence that they feel there is some guilt involved. (Not unlike “put me on the list for a pardon…”)
Also, saying “I barely knew the guy…” could sound like coaching a witness on what they should say, particularly if it’s pushing an untrue story. I guess the other question is whether the statement was made publicly enough that the witness is likely to encounter it or be told about it…
One TV commentator after another has said “the best thing a client can do is SHUT UP!” and this discussion is a good example of why.