This was (is?) a thing—he isn't making it up. When I was growing up in the UK, I remember it being considered normal and good when you caught chicken pox from other children, because it meant you finally had it out of the way. I didn't even know there was a vaccine until well into adulthood.
Still, none of this has any bearing on COVID.
ETA: Note the date of this article, which suggests that chickenpox parties are far from unusual in the UK:
Deliberately sending children to catch the virus could become a thing of the past if jab is introduced
www.theguardian.com