Imho, whiteboard tests are a good way to test a number of things.
Can the applicant
They are all important for a professional developer's every day life, so checking them in a sane context is a vital part of an interview.
Imho, the above tweet does not include enough context to conclude that the Google guys are the jerks, or if the whiteboard task was evil. It's hard to put things into relation if you only read a two-sentence rage post from one side.