The mistake here is that the person explaining is interested in things like being correct or promoting efficiency while the adversary is only interested in hierarchy and dominating the explainer within their social context. That's the miscommunication happening.

A reason is an explanation although not all explanations are reasonable.

An excuse is an attempt to justify a reason/explanation.

Excuses are used when the expiation is not reasonable.

I think this person asking you is really trying to tell you you did something the wrong way, but in a less direct manner, because directness is considered "rude" in some cultures.

More often than not it's more appropriate to say "I misunderstood, how should it have been done?" or "Sorry, I wasn't paying attention. I'll be more careful" which may or may not include an apology depending on whether you inconvenienced someone else.

A reason is a motivation to do a thing. An excuse is a reason to do the wrong thing (though not necessarily an inherently wrong thing - just anything that the other person thinks was wrong).

I really dislike rhetorical questions.

(got put in wrong place. Edited and put in correct place for proper response)

Yeah I mostly just lie and something like "I just do it the way my brain does it." Because "I don't want excuses" is all I heard for years growing up, so ok I will not provide any further to you.