That makes no sense. Having traces of THC in your system does not mean that you are still high. Same for nicotine.
I know that, but I know most companies if you are involved in an accident you get a blood test. Not saying you are high which I know you aren't, but traces of THC in your blood could still get you fired.
I used the nicotine as an example that just because a substance is legal you can still get fired. It all depends on the company.