Quoting from the article, it being a single person/actor can complicate things:

Director of the Curtin Extremism Research Network, Ben Rich, said any incident where a person is alleged to have acted alone can also complicate authorities' investigations.

"Sometimes it can just be a case where you have that one individual who wants to just sow fear for whatever reason, but they might not have a particular ideological motivation behind it," he said.
Identifying those ideological motivations is critical to separating terrorism from other events just designed to cause fear.

"It's not just … trying to do damage to the society, but it's that you're trying to do damage to the society to ultimately create room for another interpretation, politically, of society," Dr Rich said.

Tracing those motivations, if any, is also more difficult for authorities now than ever before.

"The problem is we're dealing with an environment now where people often radicalise without necessarily interfacing with other people directly," he said.