Formal word when someone goes on the attack
The respondent in example probably went on offensive by indulging in a smear campaign.
Wikipedia:
A smear campaign is an intentional, premeditated effort to undermine an individual's or group's reputation, credibility, and character. Like negative campaigning, most often smear campaigns target government officials, politicians, political candidates, and other public figures. However, private persons or groups may also become targets of smear campaigns perpetrated in companies, institutions, the legal system, and other formal groups.
Cambridge:
smear campaign noun
a planned attempt to harm the reputation of a person or company by telling lies about them: They accused competitors of mounting a smear campaign to drive them out of the market.
I think you are referring to a countercharge:
- a charge by an accused person against the accuser.
To countercharge:
- to make an accusation against (one's accuser).
Dictionary.com
If you want to point out that the countercharge is based on false assumptions you may refer to it as a :
Calumny:
- the malicious utterance of false charges or misrepresentation; slander; defamation
One term of art in psychology and criminology is DARVO.
DARVO refers to a reaction [that] perpetrators of wrong doing, particularly sexual offenders, may display in response to being held accountable for their behavior. DARVO stands for "Deny, Attack, and Reverse Victim and Offender." The perpetrator or offender may Deny the behavior, Attack the individual doing the confronting, and Reverse the roles...such that the perpetrator assumes the victim role and turns the true victim -- or the whistle blower -- into an alleged offender. This occurs, for instance, when an actually guilty perpetrator assumes the role of "falsely accused" and attacks the accuser's credibility or even blames the accuser of being the perpetrator of a false accusation.
- Jennifer J. Freyd, University of Oregon, What is DARVO? (emphasis mine)
This is quite similar to what is spoken about in the question that the OP referenced - someone who is willing to manipulate and twist facts to ensure that they win and is less concerned about justice or truth.