Child Themes

Am I right in saying this?

1) If I use a child theme and you (the developer) makes an update to the theme, even if I run any updates myself the custom changes of my child theme will remain in tact.
(I don’t quite understand why it doesn’t change because surely my child theme copies your parent theme?)
2) If I choose not to use a child theme, and you make updates it will affect my files. However, if I don’t apply the updates you made then my site will stay in tact.

Does that make sense?