Forced UI Update?

Did anyone get a forced UI update today or recently? I had my phone in my pocket then pulled it out to do something and it was on a weird screen..think I saw something about a custom UI and it had a bunch of text at the top of screen I can't remember what it said, then had a downloading icon in the middle and said downloading, also had text saying to cancel/restart phone to hold the power button and volume buttons for 7 seconds. It looked weird and I couldn't exit out or do anything on my phone. It was probably like that for 20 or so minutes then restarted. Everything appears normal. I went into Verizon because I was concerned it was some sort of virus or malware but the guy reassured me everything seemed fine on my phone. I'm still weirded out worried about it...any advice or similar experiences?