Thoughts on the whole source code leak bullshit

The source code has been out since 2018. A fake image scared people and made knowledge of it more widespread. You have nothing to fear as the image was confirmed fake.

Suppose it depends on who has the files and what their knowledge of coding is and what their intentions may be. Valve aren't completely ruling out potential problems, they are saying they can't guarantee issues won't appear and it's best to play on 'official servers' basically covering their asses.
A lot of the vulnerabilities in the build will have been patched already, but I guess this doesn't leave new ones being exposed.
Because of the profits involved, you also can't entirely rule out some form of damage control in the media by Valve.
According to some accounts the rumours have hit the player base of CS GO quite hard.

Unless you somehow downloaded a modified client onto your PC (I don't know how you would end up doing that unless you were trying to pirate tf2) then I don't see any way of hackers being able to gain access.