Someone very clearly was trying to get Dr. Sarkar fired. The PubPeer comments are only one small aspect. But the person then also (I assume anonymously) emailed his new employer to allege fraud, and then went so far as to print out these allegations and stamped them with official looking nonsense about being from the an NIH investigation (which didn't exist), and distributed them throughout Sarkar's department mail boxes.
The complaint makes a decent case for why they think pretty much all the negativity directed at this researcher is likely from one angry person. They obviously can't prove that multiple anonymous comments are from the same person, but reading the content it certainly seems likely. What is assumed to be the same person then took things way past the line of what most of us would consider ethical.
There may very well be a place for anonymous calling out of potential research misconduct. But making fraud allegations anonymously online, then printing out those comments, trying to fake them to look like an official government inquiry, and physically delivering them to the researcher's boss at his place of work isn't the way to do that. This case might be one of those cases where the anonymity should be protected at all costs out of principle, but it's a really shitty case to wave your "we're the good guys" flag for.