If you mean an Immune escape that is not a real problem for rabies because that virus has a slow evolution as you can tell from the fact that the same vaccines that were used in the 80s are still used today. Compare that for example to flu or Covid-19 vaccines where even two year old vaccine types are considered outdated and not used anymore.
They don't mean immune escape. It's either an unclear joke or pseudoscientific bullshit based on a lack of knowledge around the immune system and diseases.