Booing your own team under this scenario is a pretty common way for fans to express their desire for the team to be more aggressive. Some probably hope that it will influence the coach’s decisions and encourage him to be more aggressive later on in the game. For others, it is just good to get frustration out.
Later on, the Bengals would be faced with another fourth and short, giving Zac Taylor the opportunity to go for it rather than take the conservative route again. Given the crowd’s negative reaction earlier in the game, it was no surprise that cheers erupted when the fans realized the team was going to attempt to convert the fourth down.