The ethical rules of confidentiality apply to prospective clients, active clients and former clients in slightly different ways.
No, the attorney that was considered but not engaged may not use that information to help a future actual client. In fact, they may not represent Bob at all. It is possible the firm can represent Bob with the specific attorney walked off.
The ABA rule -
(a) A person who discusses with a lawyer the possibility of forming a client-lawyer relationship with respect to a matter is a prospective client.
(b) Even when no client-lawyer relationship ensues, a lawyer who has had discussions with a prospective client shall not use or reveal information learned in the consultation, except as Rule 1.9 would permit with respect to information of a former client.
(c) A lawyer subject to paragraph (b) shall not represent a client with interests materially adverse to those of a prospective client in the same or a substantially related matter if the lawyer received information from the prospective client that could be significantly harmful to that person in the matter, except as provided in paragraph (d). If a lawyer is disqualified from representation under this paragraph, no lawyer in a firm with which that lawyer is associated may knowingly undertake or continue representation in such a matter, except as provided in paragraph (d).
(d) When the lawyer has received disqualifying information as defined in paragraph (c), representation is permissible if:
(1) both the affected client and the prospective client have given informed consent, confirmed in writing, or: