This seems like a fairly reasonable assumption for the Briar case. An adversary would have to get a user accept a Briar link in error. Contrast with things like Signal[1] that base their trust on phone numbers.
Note that Briar groups are controlled by one moderator. Other participants of the group can not add members. Note also that Briar has the concept of introductions. So it is easy to avoid making the sort of identity errors commonly made by other schemes.
Note that Briar groups are controlled by one moderator. Other participants of the group can not add members. Note also that Briar has the concept of introductions. So it is easy to avoid making the sort of identity errors commonly made by other schemes.
[1] https://articles.59.ca/doku.php?id=em:sg