“Fish roe” is a subset of “caviar.”
The word “caviar” has traditionally been used to the gently cured eggs of various Caspian Sea sturgeon species. Other sturgeon species, as well as the roe of wholly different genuses of fish, such as paddlefish, capelin, lumpfish, salmon, and others, have been given the name.
They’re both talking about the same thing: fish eggs. However, roe refers to the actual fish eggs (or male fish sperm), whereas caviar is roe that has been salted or “cured” and then stored and aged in tins. Any caviar product sold in the United States or Canada must be made from sturgeon roe.