[Giants]

Who hit the last walk-off grand slam by a Giant?      Bobby Bonds?

Who hit the last walk-off grand slam in the franchise’s New York era?  Clue - a guy who hit a rather notable walk-off HR later the same year. 
Bobby Thomson?

Both are correct.

Including Yaz, that leaves two other SF Giants who hit walk-off grand slams….

[Giants]

Who hit the last walk-off grand slam by a Giant?      Bobby Bonds?

Who hit the last walk-off grand slam in the franchise’s New York era?  Clue - a guy who hit a rather notable walk-off HR later the same year. 
Bobby Thomson?

Both are correct.

Including Yaz, that leaves two other SF Giants who hit walk-off grand slams….