You are talking to Person B. Person B talks about something they bought from Sainsburys, only they don't say Sainsburys, they say Tesco. You both only shop at Tesco occasionally, it is on the other side of town, and it shuts early today. You notice the mistake but don't query it.
A couple of hours later, Person B has to pop out to get milk. They announce they're going to Tesco. You say, 'Sainsburys right?' Person B says, 'that's what I said.' You tell them that they didn't, and you just wanted to make sure because Tesco is closed now. They are adamant they said Sainsburys and definitely wouldn't have said Tesco because that would make no sense. When you suggest they mispoke they insist you misheard.
This is forgotten until a few days later. Person B says 'The train is after seven.' You know they actually mean 'before seven' because you have seen the train times and want to check they don't miss it. So you ask, and again they are adamant they DID say 'before seven,' they definitely said it and you misheard it. But you didn't. Person B is not an asshole or a gaslighter. Neither are you. This has happened a lot lately.
Would you worry about the fact that you were mishearing words as different or opposite words? Would you worry that Person B is absolutely certain they're speaking correctly? Person B says they were very aware of their words, shaping those words, and the memory of saying them. You know exactly what you heard. Both you and Person B have good hearing, though you have mental health issues (anxiety and depression, which are sufficiently medicated).