The attitude of praising yourself with faint deprecation may have contributed to your not interviewing well. HR have a nose for BS.
They probably just found someone with more retail sales history. Or the regional manager's niece needed a job. Why must you find some sort of technical reason for why they didn't hire you?
You should know by now that most places you apply to won't end up hiring you. There are a million different reasons for that, almost none of them are personal, and even if they are then you just say, "**** them, I didn't want to work there anyway."