How to prevent model from recognizing false Classes
I haven't actually played around with this problem, but here are a few resources:


AI.se question - Why not teach to a NN not only what is true, but
also what is not true?  
How to Make a Neural Network say "Don't Know"? (maybe try
requesting fulltext through ResearchGate )  
blog post - Making Your Neural Network Say “I Don’t Know” — Bayesian
NNs using Pyro and PyTorch


Edit: I just found the following questions here on DS.se:


Multi Class + Negative Class Image Classification Strategies
Fine-tuning a CNN for recognizing two classes, but also being able to tell if none of them is present in an image