What was Potifar's wife referring to when she said "ka'Devarim ha'Eileh"?
Rashi (from Bereishis Rabah 87:9): At a time of intimacy 1 with Potifar, she said 'your slave did things like this to me.'
Shir Ma'on (17): She said roughly, but not exactly, like she told the household, lest Potifar realize that she lies. If witnesses say exactly the same words, their testimony is disqualified, lest they coordinated to say the same lie. In proper testimony, each witness speaks in his style 2 , and they begin the account from different points.
Ramban #1: She was referring, not to anything that they were doing, but to the things that were mentioned above.
Ramban #2: She simply told him the same as she told the members of her household. 3
Ha'Emek Davar: Potifar could not believe that Yosef began with such a despicable sporting. She answered that several times before, he was frivolous with me, but I did not pay attention until this sporting.
Even though here she speaks in both cases, one speaks differently to her husband than to her household, and amidst greater agitation right after a shocking experience, than later, after calming down. (PF)
Ramban: The 'Kaf'' (in "ka'Devarim') is unneeded (really, it was exactly the same) like we find for example above (24:28).
Why was Potifar angry?
Seforno: He was angry with his wife for accusing him of bringing an Ish Ivri into the house to make fun of them - because he believed Yosef more than he believed his wife, whom he concluded had lied about Yosef. 1 And he placed Yosef in jail out of respect for her, as if he actually believed her. 2
Ohr ha'Chayim: He did not believe her to punish Yosef like a slave who puts his eyes on his master's wife, but her words somewhat moved him.
Malbim: She said that he already lied with her. Potifar did not believe that Yosef would be so bold to do so. He was not angry at Yosef; if he were, he would have killed him! Rather, he truly understood the matter; he was angry that now he cannot keep Yosef in his house.
Alshich: He understood that his wife lied. (Refer to 39:17:151:1.)
Rashi (from Bereishis Rabah 87:9) writes that at a time of intimacy with Potifar, she said "your slave did things like this to me." Potifar was a eunuch and could not have Bi'ah!
Ramban, Da'as Zekenim #1, Hadar Zekenim (17) #1: The Midrash does not refer to actual Bi'ah, rather, to the foreplay that leads to it.
Da'as Zekenim #2, Hadar Zekenim (17) #2, Riva (17): He was partially castrated. He could get heated enough to be intimate with a female, but not with a male.
Da'as Zekenim #3: He was castrated only when he wanted to be intimate with Yosef.
Moshav Zekenim: He was able to be intimate, but not to ejaculate. 1
If so, he could still sodomize Yosef! Perhaps he was too ashamed to, lest Yosef realize Potifar's impotency.