He needs to get a court letter confirming some kind of Infringement first before google Acts on your site.
Don't compare your case to Big movie industries and software companies that can have google take down their contents or infringing URLS since those cases are pretty much obvious and money talks.
Google won't even respond to this guy without a Court Notice. Had few experiences in similar level and even worse case than yours and google never even responded. "This a confirmed case, not from my words but from lawyers that we hire in the US and EU for such cases"
Sit back, relax, tell them you bought a readymade theme from some place and modified it to your requirements which coincidently matches their site so tell them to back off before they get hurt in a lawsuit from you and your lawyers, and please sound solid and not silly in your emails to them.