@Chinajan
//If the OP wished to continue to use Twitter it would be a simple matter to change the contact email address to a different, spare one.//
You have slightly lost me there. "The contact email address" is not something I recognise as a Twitter feature. What twitter calls DMs (direct messages) are still addresed to the person's Twitter handle which, in many cases is a pseudonym, as we have here, on AB.
Late adopters, myself among them, are encouraged during the signup procedure to create an account *under their real name*, since this discourages trolling and actionable abuse. The need to add digits after the name only arises when the initial attempt reveals someone else has that username already and it asks you to make the ID unique, in some way.
Whilst tacking digits on the end does achieve this, the first name and surname are still "Joe Bloggs" and the Twitter search engine throws up matches while you are typing. You only need to have an uncommon first and second name combination for the search to find you before any of the digits are needed to further narrow the search. Of course a close relative, who knew of the meeting with the celebrity would be in search of the OPer for that very reason.
Having a photo of yourself as an avatar helps people who know you pick you out from all the namesakes, of course. Not an issue here, as that is a whole lot of palaver for someone who only wanted to make 1 tweet in the first place.
Despite all the above waffle, even if you opt for a non-real-world username, you are still instantly 'discoverable' by way of choosing to use the email all your friends/rellys know you by to sign up. They only tell you about this feature after it's too late to change it and, for some, setting up an auxiliary email account, via their ISP's website and tweaking their mail-reader settings, to suit, is just an extra half hour's hassle they can live without.
Incidentally, posting a tweet with no avatar is referred to as "posting as an egg". So many trolls have posted as "eggs", setting up throwaway emails and throwaway Twitter acounts to do so, that many, if not all, celebs adopt a policy of "never reply to egg posts". So that's what caused the lack of response, IMHO.
//and felt the need to set up a wee twitter account to say how it made my day.//
But they know this and it takes up their time to read hundreds of such Tweets, I should imagine. It's a lot simpler to just fawn all over them and gush incoherently about how much you love their work.
No. The Twitter account is about *you*. A nice/not nice thing happens in your life so you make sure everyone knows about it.