This seems to be more a question of understanding the difference between a human being and an angel.
The word, כף, has multiple meanings (arch, hollow, palm of hand, sole of foot, etc.) and one must look at the specific context to understand the meaning.
Human beings have arms and legs. So in regard to Yaacov Avinu, it is clearly referring to his thigh and ...
Rashi to Genesis 18:10 (the first verse you cite with "I will return to you") explains that the angel is speaking on behalf of G-d.
שוב אשוב. לֹא בִשְּׂרוֹ הַמַּלְאָךְ שֶׁיָּשׁוּב אֵלָיו, אֶלָּא בִשְׁלִיחוּתוֹ שֶׁל מָקוֹם אָמַר לוֹ, כְּמוֹ וַיֹּאמֶר לָהּ מַלְאַךְ ה' הַרְבָּה אַרְבֶּה, וְהוּא אֵין בְּיָדוֹ לְהַרְבּוֹת, אֶלָּא בִּשְׁלִיחוּתוֹ שֶׁל מָקוֹם, ...
Rabbi Uri Sherqi suggests that Terah was originally from כנען, which would make it likely that Abraham was born there and/or raised with a Canaanite ethnicity. Why else would they specifically seek to go there?
Alternatively, Abraham is a Shemite as is written explicitly in the Torah. This question could benefit from a precise definition for “ethnicity”.
This is two questions:
1) How could the Torah describe the city of Ur as being of the Chaldeans if they didn't exist yet?
The Torah clearly describes a city in which Avraham and his father resided as being called "Ur Kasdim", so either
a) The Torah is using a "borrowed" and contemporary-to-a-future-time name (Chaldeans) in place of some proto-Babylonian ...