mobile

So this is going to be a stupid question, but I need a definitive answer.

I had to go to the Best Buy Samsung Experience area for help with getting the Lollipop OTA to install. I won't go into the details about that, but I will about one thing that happened that has been bugging me for a couple weeks now.

The first thing the Samsung "expert" did was unlock my phone to see Nova Launcher on my phone. He then looked at me and said "this isn't Samsung's launcher. The system was modified so I can't help you." I then had to show him that Nova Launcher was just an app that was downloaded from the Play Store.

I thought it ridiculous that I had to even do this. That I basically knew more than the "expert" and was immediately turned away due to running an app that doesn't require root. In the end, I did get help, but had to uninstall Nova first because he kept blaming Nova for the update not installing (and the update still wouldn't install after uninstalling).

So my question is this:
Does running Nova Launcher somehow void warranty? Was the "expert's" initial refusal to give me service justified?

BTW:
This wasn't the first time that I knew more than the Samsung "experts." When I was shopping for my Note 10.1 (2014 ed), I tried to confirm with one of the "experts" that the octa-core cpu was in the US models. (It isnt a true octa-core. It runs at either a lower powered quad-core configuration, or a higher powered one, depending on the aituation). The guy told me that the US wifi versions only have quad-core cpus and that I'd need an international version in order to get the octa-core. I ended up emailing Samsung to confirm this because it didnt seem right to me. They told me that all wifi versions of the tablet (at the time) had the octa-core Exynos cpu. They seemed surprised that the guy told me this. In the end, Best Buy lost my business for this purchase. I ended up buying from Samsung directly (they had a better price anyways lol).