וַיָּשִׂ֥ימוּ ל֛וֹ לְבַדּ֖וֹ וְלָהֶ֣ם לְבַדָּ֑ם וְלַמִּצְרִ֞ים הָאֹכְלִ֤ים אִתּוֹ֙ לְבַדָּ֔ם כִּי֩ לֹ֨א יוּכְל֜וּן הַמִּצְרִ֗ים לֶאֱכֹ֤ל אֶת־הָֽעִבְרִים֙ לֶ֔חֶם כִּי־תוֹעֵבָ֥ה הִ֖וא לְמִצְרָֽיִם׃
他們為約瑟單獨擺了一席，為他的兄弟們單獨擺了一席，也為與約瑟一同吃飯的埃及人單獨擺了一席，因為埃及人不可以和希伯來人一同吃飯；這是埃及人所厭惡的事。
Rashi
כי תועבה היא FOR THAT IS AN ABOMINATION — it is a hateful thing to the Egyptians to eat together with the Hebrews. Onkelos states a reason for this.
Rashbam
It would be spitting and a shame for the Egyptians to eat with the people from across the river [ever hanahar], since those people were contemptible in their eyes, and the Egyptians were haughty, as it is written (Isa. 30:7), "I call this, 'They are a threat that has ceased.'" Similarly (Gen. 46:34), "For all shepherds are abhorrent to Egyptians" -- they despised shepherds because sheep were contemptible in their eyes, as it is written (Exod. 8:22), "If we sacrifice that which is untouchable to the Egyptians before their very eyes, will they not stone us!" That which is repulsive to the Egyptians and disgusting, if we sacrifice it before their eyes to our Rock, won't they despise us, stoning us in a shaming way, as we find (II Sam. 15:5-6), "Shim'i ben Geira came out from there, hurling insults as he came. He threw stones" He cursed David and stoned with dirt, in a shaming way.
Radak
וישימו לו לבדו, they served him separately as a symbol of his exalted position.