How do MENSA invitations work?

I once did a quiz for MENSA and they sent me a typed invite to write their test. Do they send everyone this letter?

Mensa

Are you perhaps a MENSA member? It looks to be quite stimulating with the socials etc. that they offer. As they sent me a brochure. I didn’t take the invite since I’d rather not know I was not MENSA material. If you are a MENSA member how is it going?

(I was surprised really since on most IQ tests (although I know MENSA’s are not IQ tests) I normally score just above retarded). loll