Lem was an honorary member of Science Fiction and Fantasy Writers of America until his work was published in the United States and he was eligible for regular membership. He was disappointed with the loss of honorary membership and felt it was due to the controversial nature of some of his work. Although a SFWA member offered to pay for this Active Membership, Lem declined the offer.
I am sure that common public image of this "Lem affair" is:
1. Group of US SF writers, lead by Ph. Jose Farmer, asks for Lem's expelling from SFWA (because of his statements about US science firction, state din i.e. first chapter of Fantastika and Futurologia).
2. To avoid shame, SFWA finds the legal way, and decides - because Lem's work were printed in US - doesn't need to be honorary member, but full time regular member. In this way, Lem will stay the member (as locally published author), and he will lost honorary membership, so both sides will be happy
3. Lem removes the idea ( = he loses honorary membership, and he doesn't accept regular membership)
That's the main outline of affair as presented in many books, articles, histories, and also on this site.
So, the statement that "Lem was an honorary member of Science Fiction and Fantasy Writers of America until his work was published in the United States and he was eligible for regular membership" but he "was disappointed with the loss of honorary membership" - that doesn't seem like diplomacy, but obvious lie.