To everyone arguing if this was or wasn't a Swatting, we don't know. This could be a Canadian equivalent of a Swatting with preparation or it could be the results of an investigation of using a handgun for a crime. Considering he wasn't charged and posted bail, as per the London Police Service, we can assume the threats and messages were faked.
To get the warrant, this falls under the red flag laws, a one-party court hearing the police applies for, shows the evidence they have to the judge, and they sign off on it. The police know what they need to win this one-party hearing, so if they received proof of threats to the councilors from a sender, that gives them enough to get started.
The original warrant has seizure of phones and computers, so its expected that they will grab them and seize them. After searching through his computer and phone, and if they find nothing, then they will be returned. The reason they are still treating this as a case is simple, the councilors received threat from person A, and they are checking through person A's material to see if the threat did come from there.
The police do not know this is fake, they might even think Keffals has a multiple personality disorder, alter egos of Lucas and Clara, so they were pushing on the Lucas questioning in their interrogations to see if that's what it was.
Most likely, this was a well done swatting, that took some research or knowledge on what would result in computer seizure from Keffals. The police are doing a standard job, as they firmly believed that a threat was coming from Keffals and they are just going to do research to see if the threat was credible. If they find incrimination information, they can pursue it although if they also find that the original threats were not from him, then it'll be hard to admit as evidence.