Chapter 695 cover: Caribou seems confuse while holding a meat pie box. Meat is the favorite food of Luffy, and Pie is the favorite food of Blackbeard. Oda might tell us at first that Caribou is confuse if he will join the Strawhat Pirates or Blackbeard Pirates.
Chapter 700 cover: Caribou is hiding in a war while holding the meat pie box and the meat was shown in the panel. Basically means Caribou is hiding in the Strawhats' ship during Wano.
Chapter 708: Grandma show Caribou a picture of her grandson Gaburu, who was the captain of Revolutionary Militia. As per One Piece Wiki "Gaburu greatly resembled Caribou, as his subordinates easily mistook the pirate for him. The only differences between the two are that Gaburu lacked a [black] beard and Caribou's signature cowlick. Gaburu also wore a green beret with a red star much like his subordinates." If you look at the picture, Gaburu also resembles to Teach, even in the hat (though different color). Gaburu is respected by the person Caribou respects, which is Grandma in this case. Maybe, there is a person that Caribou highly respects who is looking up for Teach, which made him a fanboy of Blackbeard.
Chapter 729: Caribou went to a departing black ship with an image of him holding the meat pie box, showing pie in the panel. This might be the indication that Caribou will join the Blackbeard Pirates. He chose Pie over Meat.
Caribou's decision to join the Blackbeard Pirates over the Straw Hat Pirates is hinted at through manga covers: In Chapter 695, he appears conflicted holding a meat pie box, symbolizing the dilemma between Luffy and Blackbeard, Chapter 700 shows him hiding on the Straw Hats' ship during Wano, still holding the pie box, Chapter 708 reveals his admiration for Gaburu, a revolutionary captain resembling Blackbeard and Finally, in Chapter 729, he boards a black ship, choosing pie over meat, indicating his decision to join Blackbeard.