It means you are taking okay care of your Tamagotchi! Training is what helps decide whether or not you will have a selfish Tamagotchi. You'll want to keep this up! Low training can get to your Tama. High training will make it behave well!
Here is a little chart I just thought of:
Bars: 1-3
Meaning: You aren't taking care of Tama to good. (Games=training!)
Pic: [|||------] or [||-------] or [|--------]
Bars: 4-6
Meaning: You're taking okay care of your Tama.
Pic: [||||-----] or [|||||----] or [||||||---]
Bars: 7-9
Meaning: You are taking EXCELLENT care of your Tamagotchi!!
I htink you're right. But that applies most to adults, cause the babies, are new and you can take care of them very much but don't have as much experiance as adults.