Virtually no company regularly pays cash anymore. Payroll is presumably mostly direct deposit and maybe some checks. Probably outsourced too, but don't know. Factories like that usually pay Friday on a weekly basis. However, it's possible they were biweekly.

As for your bomb suggestion, it's possible, but would be one heck of a big one to do that much damage. Looks like a natural gas explosion. However, anything is possible. Would expect within a few days the authorities will release a statement of the probable cause.

On a related note, the Wyomissing Post Office also experienced a natural gas explosion about 40 years ago. Such incidents are very rare, but happens more than they should. For residential, all electric is a realistic option, but for manufacturing, often not viable.

Rambling on. In short, near certain an accident.