How to tell the difference between food poisoning and stomach bug? only vomited once after eating bad meat, not sure if contagious.

Diarrhea: Usually if you have a stomach bug or gastroenteritis you will also have diarrhea. Especially if you have bloody stool that is an indication of a gut infection. However, if you have vomiting alone and quick improvement that is more likely "food poisoning" or bacterial toxins in your food. I would throw out the bad meat and make sure to wash your hands well since gut infections are very contagious.