Because they contain a lot of stuff that isn't directly related to the issue and is easily verified by other people. Simple routine stuff which can be matched up with who was where at what time and said and did what. Also it's not like there are only these screenshots of texts. This was going on for a while and would surely be noticed by other people. The person in question reported it to HR and has been on sick leave ever since. This person also has deleted/set private all of their public profiles. The person also notified several people while this was going on, sharing the screenshots. This is just evidence to corroborate all of the other things that were already known by multiple people.

Of course there is no way to be absolutely sure of this, unless either really hard proof is found or both parties confirm this is what happened. But given the huge difference in power between the two parties, the party with the least power needs to be protected. Especially these days where anything can be faked.

It's not up to us to make judgment, that's for a judge to do. And a judge will take this evidence for what it is, screenshots that could have been faked. But if the information therein can be confirmed via multiple ways, a judge may decide to take them at face value. A defense might employ an expert which can indicate if these files were faked or not.

So no, this isn't evidence and it isn't faked. We simply can't know for sure at this point. What they are however is a starting point to investigate further, for more parties to call for a proper investigation. This investigation can lead to more evidence, or it can lead to it being nothing in the end.

Who knows what will happen. I'm personally aren't willing to go so far as to say these files can be faked so they must be fake. One thing does not automatically mean another thing. I feel whoever released these had the intention of not letting this get swept under the rug, and it seems to have worked. I also don't think it was the victim that released these, it's probably a nightmare for her. Imagine having your dream job at an F1 team and losing your job over something like this. Horrible.