If you truly believe an operation is a serious risk to your career or safety, who cares what the employee manual says, you should have given 4hrs notice of leaving not 4 weeks.
If you are convinced you made the proper professional decision in the interest of both you and the company, who cares what they call it.
If you're convinced you are in the right, who cares what they tell your next employer, if your decision bothers your future employer, you don't want to go work for them anyhow.
So the real question is, "did I make a good decision?" If you're convinced that the answer is yes, then how the other side responds is irrelevant, just move on and don't look back.