Nowhere near that scale, but we had one office closed, the CEO met with each team personally, then made a wider announcement to the company once all the severance and other things were fully hashed out, and new roles could be found for folks that could relocate.

Probably the right thing would have been smaller lay offs a while ago, they must have seen this coming.

Usually fed down the chain of command. Execs tell managers who tell their people, HR is usually involved too. If the managers are also involved, it's a bigger affair

It's rarely a surprise in my experience (eg: new owners/investors are sniffing around for months). Announcement of the acquisition/investment is often made, mentioning that certain business units will need to be 'optimized' or some other vague term.

Yes, in my company their aim was to complete the redundancies as fast as possible, and it took about one week. One on one meetings are held with HR - I don't believe line management was even involved in the meetings. The employee leaves the office immediately.

The bottom line is the getting fired is, almost always, bad news. Sure delivery matters but if he was announcing a raise, no one would have questioned the manner. So unless he had some major financial aid for the laid off...

Big meeting with HR or CEO is completely normal.

Preferably followed up with various smaller meetings, but those aren't legally required everywhere.