I think her Mom is just saying something like "please don't call us with a tip saying your friend kind of knows a guy who may have heard something about what happened that night, but you can't give any names, details, or ways to contact anyone about the tip." That isn't helpful in any way. I don't think she's saying the tipster has to provide all of their personal information. But you can't really follow up on a tip with no specifics. I'm sure if someone called saying "I can't tell you why I know this, but you should search XYZ Park north of the walking trail" that would be followed up on without needing to know the caller's identity and contact info.