Did G-man killed Cave Johnson?

As we see in Portal Testing Initiative DLC of Portal 2 there are an alternate timeline of our standard Half-life universe were Cave Johnson prevented the Black Mesa catastrophe by buying the company and preventing the Xen crystal from being tested, thus frustating G-man's plan to trigger a resonance cascade to further his plan to include humanity in the fight against the Combine.

With this information and the information we have at the end of Half-Life Alyx about G-man being able to travel between time, space and timelines, we can say G-man took action in order to make the necessary adjustments, so that his plan would go ahead as his employers wanted it to, it was necessary to ruin and kill the CEO of Aperture Laboratories.

What do you think?