He did not cause a serious hazmat situation. The authorities decided to evacuate a street, and are responsible for the seriousness of their over-reaction.

The packages were labelled correctly, and blocked at the border, and USPS delivered them anyway. He offered to send them back as soon as he was made aware they weren’t permitted.

The real failure here is at the border, where they were flagged and then let through, followed by the absurd over reaction of the authorities to a situation they’d enabled

If you read more it was border control making a security theater (2months after they were aware of the situation), instead of calling appropriate government agency that are actually qualified to deal with radioactive material.

If there was a real threat why did they wait so long before evacuation, why didn't they call the appropriate government agency whose job is dealing with radioactive stuff?

The next paragraph also reads...

> However, The Guardian reported that Lidden’s solicitor, John Sutton, had criticised the Border Force for how it had handled the incident, describing it as a ‘massive over-reaction’ because the quantities of material were so small they were safe to eat. He reportedly said that he had been contacted by scientists all around the world saying that the case was ‘ridiculous’.