I sent a cease and desist to a startup company that used some coding work I was informally contracted (aka no formal contracts/agreements) to do, but ended up never getting compensated for. There was never any lawsuit, nobody was sued, I simply had the letter sent (drafted and sent by a lawyer).

The owner of the startup sent a letter back saying that "New York State has advised me to consider legal action for malicious harm" and that my work was "unjust enrichment". This letter does not seem to have been drafted by any firm or lawyer. The lawyer that drafted my cease and desist said it seemed baseless and was not a claim and that I could just ignore it and not respond, which I have done.

The letter seems to be a scare tactic sent by the pissed off CEO, but was just wondering what the opinions of others are. What does "malicious harm" even mean in a legal sense (if anything)? Is that really something that could come from me sending a simple cease and desist?