No, people were explicitly saying that this stuff never normally happens, strongly implying that it could only happen because of the attackers background (maybe that was a factor. We don't know). A DUP member said that it was the most horrific violence in NI he could remember. Hmmmm. When people point out other perpetrators who did similar things, then the argument " but we can't do anything about them being here" is brought out. It's true but it's not the original argument that was made. And besides, while you can't deport (eg) white British rapists, murderers etc you can look at the possible failures in the system that allowed it. By focusing only on race/immigration as the means to reduce violence it stops any real change to eg police attitudes towards working class victims of CSA, mental health provision, sectioning. It creates a false sense of security. And when people do try to talk about it/about the possible wider issues or how to fix the problem they are shouted down and told they don't care because they aren't sticking to only immigration as a topic.
The other reason it's relevant is because people were suggesting the Belfast attack wasn't being reported as much because of the race of the perpetrator. Two tier might have been thrown around. A very similar case that was reported but certainly not reported more heavily is relevant to that argument.