My 16 year old beat up someone

My son got into a fight and I never knew about it. It was a couple weeks ago and somehow the mom is just finding out now who beat up her son because she came to my door for a confrontation. My son is 16, hers is 17 or 18. I asked him did he beat up her son and my son said yes. I asked why and he was on his phone saying "Because he's a little bitch." I took the phone away and I wanted to know what happened. He told me(he had text messages to backup some of this) that he wouldn't leave him alone and had been fucking with him for a year because my son is a little goth emo and paints his nails black and this boy was harassing him. They started arguing and he said what this other boy said to him is that his older brother went to prison for fucking little f*gg*ts and he's going to beat my son's ass and then let his brother fuck him bloody until he's begging for death. This was something he texted my child. So my son just beat his ass the next time he saw him. And beat his ass bad. Then he told the boys mom "I beat your son's ass. He's a little bitch. And you have your registered pedophile son living with you and other minors so you have other shit to worry about." I didn't say anything because I was still taken back by those horrid text messages. The mom just told me to keep my kids tf away from hers and left. I don't want my son handling problems with violence and he's usually not a violent person. I asked why he resorted to violence he said the kid threatened him like that so he gave him a chance to prove he wasn't "all bark" and he lost. My husband is proud of him. He beat up this kid badly from the sounds of it. He had to get an eye brow stitch from what the mom said. I don't want to praise this behavior but I also don't want to punish him because those were fucked text messages.