A persons disposition refers to the persons mood or temperament, temper, character, personality.
The meaning of the word disposition refers to and also implies customary moods and attitude toward the life around one.
For example the Donald Duck Song which says "Who's got the sweetest Disposition?" they are saying that Donald duck as a sweet temperament and mood.
Although Donald Duck can be moody at times he's a sweet duck after all.
So if someone says you have a sweet disposition it's a good thing they are saying about you.
I tell my 2 year old boy that he has a sweet disposition although right now he does not know what disposition is but he knows what the word sweet means.
He is very sweet and I love him so dearly even though he can be a pain at times and makes me want to pull my hair out sometimes.
I still love him regardless and I'm glad I have him.