There are definitely some acting as spokespeople (even if they claim otherwise), but there are also quite a few who are just, you know, incredibly biased fans of their employer, who like to defend them on topics unrelated to their job.
But when a tech company has 100,000 employees, it's not particularly surprising to see a good number of them on a tech forum. ;)
They might just say, 'That seems silly!', 'You're a nut', 'Do you have a source other than yourself'. Or they might just downvote stories that have a negative effect on their income.
You've got 100k people working at google and many of them are going to be active on this type of forum. The same goes for the other big guys that have a ton of employees
https://www.theguardian.com/technology/2018/nov/21/facebook-...
This is all quite in the open.