When I was in college, I was home for the summer and the police came to my house to do a welfare check. They stated a 911 call had come from my number and they couldn't get through when they tried to call back. They asked who was in the home and if everything was okay. I told them it was, but you could tell they were looking for any hint that I was being threatened. After I told them I'd been on the computer, they ended up asking if I had a dial up connection to the internet. Apparently sometimes dial up will go wacky and dial 911. They never came in the house, nor did I invite them in. While they were in uniform, and I lived in a VERY safe neighborhood, I could not see the parking area from the door. It was only my mother and I in the home, and I honestly did not know if it was someone trying to gain access to our home. People have been known to dress as police officers to commit crimes. Granted, I knew where my mom was in the house, but even if I didn't, I probably wouldn't have checked until they were gone. Or I would have asked them to please stay outside while I checked.
As for sleeping through something, we don't know if people were still up. The daughter may have gone to bed before anyone else, and since others were still partying, they didn't hear anything. Also, even when I don't drink, I can sleep through anything (or used to, before I became a mom!). I hated when I stayed alone because I was always afraid someone would break in and I wouldn't hear it. I've fallen out of bed, onto a metal vent, and not woken up. My DH, when he drinks, will not wake up. He rolled over on top of me after drinking one night (before becoming a dad), and I had to shimmy my way out because nothing would wake him up. So I do think it is possible that no one heard anything.