No one suggested that one question and a refusal was an offence - but you said that should be the end of the matter.And you've not shown me that asking someone on a date these days can offend someone. Isn't that what this started as?
Is he, therefore, not allowed to ever speak to you again?
Is he not allowed to "try again"? If yes, then how many times?
Have you never heard "faint heart never won fair lady"? Totally outmoded?
So, what constitutes you being alarmed and distressed?
Remember - no improper behaviour at any time.