Sam, that is a Gemara in Kedushin if I’m not mistaken.
And mistaken I was. It is in Yevamos 32b and the Gilyon Hashas points to something similar in Shvuos 26.
I’m not sure Eilu Va’eilu should apply to what they think they heard. The idea of Eilu Va’eilu is not about never being wrong. It is about Torah Lishma being true. It’s about being Mechaven El Ha’emes. The Gemara in Bava Basra calls it a Nevua.
There is another point to be made. Torah Shebaal Peh is not just detective work, trying to guess what Hashem wanted. When the Chachamim learn a certain way, that becomes the Ratzon Hashem. That is why Hashem quotes them.
Hashem gave the Torah as would be interpreted by the Chachamim. Even if they argue about Keilim of the Mikdash, and the Keili was only built like the Shita of one of them, that just means that we didn’t Pasken like that. It doesn’t take away from the validity of the Shita.
In the case of Esther’s Kavana, in Megilla, and Pilegesh begiv’a, in Gittin, since they were Me’ayin and learned Lishma, they were Machaven to the Truth. Therefore, it had to be in the fact.
In other words, in a Halachic Machlokes about something in the past you don’t have to find a way that both happened, since it is no different than a Machlokes about Psak of the present and future. But, a Machlokes about a story, especially when it is based on learning a Pasuk, the event is Sovel both Shitos.