Any Firearms course brings up the same subject. Here is the deal. If you are selected for inspection as a firearms owner, and you happen to have your Airsoft not locked up, then yes, they could try to argue with you that you're breaking a law. I had a firearm instructor tell me that they dropped by his house, and attempted to argue that they could charge him because he had an a few Airsoft guns in the house that his kids and him play with on their property.
Nothing came of it outside of that conversation.
Seems every firearm instructor brings this up in their lecture.
I wouldn't worry about it.