I have two possible theories.
1. Timon and Pumbaa are Bunga's "uncles". Meaning they are friend's of his family or he regards them as family though they aren't blood related. For example, I call a few of my Dad's friend's uncles as they have been around all my life and are good friends of the family. Or it may not be Timon and Pumbaa but another creature that Bunga holds in high regards. A bit like Milla has suggested (which would give the film a nice feel)
2. It IS Bunga's blood uncles that say this.
However, there is something that is puzzling me. Does the Lon Guard take place after or during Lion King 2? If after....didn't Timon and Pumbaa come up with a new moto and ditch the whole Hakuna Matata (honestly that annoyed me so much)? If so.....then maybe theory one isn't true/doesn't make sense.