How do you catch Chicken pox from shingles?

I just found out that my friend has shingles, he got me to look at his back a few times, I don’t believe I touched any of the blisters but may have touched the rash.
I know hear that you can catch chicken pox from shingles.
In order for this to happen do you need to be exposed to the blisters?
Could I have caught chicken pox from him?
I’m pretty sure I didn’t touch the rash but am pretty concerned.
I’m not sure if i’ve had chicken pox or not….

thanks!