Hmm, that’s weird.
It shouldn’t change any defaults – especially not in ACR.
The only thing I can think of is if there isn’t any existing raw profiles for a camera or scanner model, it’s possible when the Negative Lab Pro profile gets added that it would become the default sort of de-facto, since there isn’t anything else there.
The other possibility is that if you edited the raw file in Lightroom using Negative Lab Pro, and you have it set to sync the metadata to the file, if the camera profile in Lightroom is set to Negative Lab Pro, then it will also be set to Negative Lab Pro camera profile when you open ACR.
Just note that if you remove the camera profiles, Negative Lab Pro will no longer be able to access the correct profiles for your RAW camera scans (or vuescan/silverfast RAW DNG scans) and that will impact conversion quality.