The brands which manufacture smart fridges usually have safety measures which prevent harm arising from hacked appliances. Furthermore, fridges are not really obvious targets for hackers. Instances of smart fridges being hacked are very rare, with far less reported than for phones, PCs or smart security systems.
However, that's not to say there's no risk at all. There are some instances of hackers infecting smart fridge software with nasty viruses which could cause all manner of problems, especially when the fridge is used as a 'weak spot' to 'hop' onto other devices on the same Wi-Fi network.