My guess is a lone nut-job.
I agree with you assessment. This smacks to me of a political motive, not a religious one. Lone-wolf nutjob.
I’d say small group (along the lines of McVeigh and his couple of helpers) than lone wolf.
A pipe bomb, package bomb, yeah lone-wolf sounds right. A car bomb? A truck? Logistically speaking, it just seems beyond one guy.