It's an idiom rather than a proverb
Thank you
very much for teaching me that. Those two words always confuse me.
***
CAUTION: NOT A TEACHER
My dear fellow learners,
I have found a book in Google "books" that explains the difference, and I wanted to share its ideas with you. I hope that I understood the book correctly.
AN IDIOM
(1) The words do
not reflect the literal (actual) meanings of the words.
(a) I guess it means that you canNOT literally (really) kill two birds with one stone.
(2) You can often change the tense:
We will kill two birds ....
We killed two birds ....
A PROVERB
(3) It is more "frozen."
(a) I guess that it means you may NOT change the tense.
(b) It is often literal. That is, it can really mean what it says. For example,
"An apple a day keeps the doctor away." That is, if you eat an apple a day,
you may not get sick. (Because apples reportedly contain some good vitamins.)
(c) A proverb is usually a
complete sentence.
Credit:
Lexicographic Description of English (1986) by Morton and Evelyn Benson.
P.S. I forgot to report something else that Mr. and Mts. Benson said:
A proverb often reflects folk wisdom or an alleged general truth.
I think that it means a proverb often expresses an idea about life or how to live life.
"Folk wisdom" refers to the wisdom (the understanding of how to live life correctly)
that human beings have learned during the thousands of years
that they have been on this planet.