Hola Larry

Yes, you are right. When we say: 

this implies that it is a "result", for example, they have gone on a diet and as a result they became thinner.

Or sometimes it can imply an element of surprise:

As a common example I can mention this typical sentence that we say to other people's children:

This is something that you realise when you haven't seen your friends' kids for some time and you express surprise at their change. 

If we were using all these sentences with ser, not estar, then we'd be expressing a permanent quality. 

I hope this helps,

Un saludo

Inma

Hi Larry

And I do agree with you in not going to the general rule about ser and estar for either permanent or non-permanent. This is why I explained the specific usage of estar in that case (result/surprise), but as a contrast to that case (estar delgado/ser delgado) I thought it was worth mentioning that if you change the verb to "ser" then you are talking about a permanent characteristic of a person without bearing in mind whether that person was thin before or not. We have a basic lesson on A1 about using "ser" to describe something/someone's permanent/essential characteristic. We have this basic lesson at the beginning of our content because this is the type of sentence you learn when using the verb "ser". Then you move on and learn about other specific uses of both verbs "ser" and "estar". We have lots of different specific lessons about these verbs without going into the general permanent/non-permanent. 

Here is a list of them:

Estar when talking about locations

Estar for physical condition

Estar when talking about feelings and emotions

Ser to describe relationships

Ser to express essential characteristics

Ser to express origin or nationality

I hope this helps,

Saludos

Inma