This is a blurry situation for both me and my boyfriend?

So my boyfriend and I were sitting together in a classroom at lunch time, ready to watch a movie in his laptop. He keeps all the movie files in his external memory hard drive which I was holding and connected to his laptop. In one instance I accidentally moved the laptop and the external disk plugged out of the slot and fell on the floor. I then could've sworn I heard my boyfriend mumble/say "fucking (and then my name)" all together. I felt super insulted but didn't say it in the moment. Later that day I brought it up and he looked at me so funny when I told him about the insult I heard him say. He told me he didn't say that, which came to me as a surprise because I could've sworn I heard it clearly. My boyfriend is usually very open to talking about situations and doesn't lie (he's very honest) so it was very weird to hear him say he did't recall insulting me. He tried to make memory but he told me he just didn't remember saying that, which brings me to my next question. Could he had said it without noticing? Could I have heard something wrong or that he didn't actually say? Insults in our relationship are VERY unusual, so is cursing. He has only insulted me ONCE in our 3 year relationship and it was because I kind of insulted him moments before. I'm saying this because I think you guys should know that he is not the insulting type, nor am I. I've heard a saying that says: People hear what they want to hear, and believe what they want to believe. The mind can create false moments/memories. I am usually very fearful of being hurt in general so maybe this irrational fear I have may have played my mind in this situation? Maybe my boyfriend actually said this and just doesn't remember or didn't realize it? Should I just forget about this uncertain moment and give him the benefit of the doubt? Or should I trust my memory over what he didn't do?
This is a blurry situation for both me and my boyfriend?
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