Earlier quoted context omitted.
They won’t automatically know, but: 1) Anyone in the industry presumably knows about this news. If someone’s end date at Activision Blizzard is January 2022, they’re going to have a strong suspicion. 2) Backchannel reference checks (very warranted in this case) will likely confirm it. Activision Blizzard wouldn’t confirm anything other than start and end dates and any candidate-provided references are going to say go…
A lot of companies will also say if the former employee is eligible to be employed there again. A negative on that plus a January separation date won't look good for those folks.
I suppose that may mean something if you're playing detective with a former Blizzard employee's resume, but I'd be cautious in reading too much into "if the former employee is eligible to be employed there again" generally. I know of a company where HR policy is that all involuntary separations are ineligible for rehire, including things like downsizing layoffs.