Though there was also a gotcha reaction at the time from some when the murderer was then said to be of a Christian background.
I don't that calling out people for lying by providing factually correct information can ever be considered to be a 'gotcha'.
The lies were that the attacker was called Ali Al-Shakiri, that he was a muslim immigrant, an asylum seeker and had recently arrived on a small boat. Non of this was true.
He is a British citizen, born in Cardiff to Rwandan immigrants. Now the population of Rwanda is over 90% christian so it is a pretty good bet that he came from a christian background. But I can be even more confident as my niece was actually in the same class as him in primary school - a catholic school in Cardiff where the family were well known to the catholic community as they were regular worshippers at the same church my in-laws attend.
Now he might have converted to islam later (although I don't think we know that), but that still wouldn't change the fact that he was from a christian background.
Have we really got to the point where everyone is entitled to their own 'fact' that calling out lies with evidence is seen as 'gotcha'. If so, heaven help us.