Like Krysalyss, I think it's most likely that he was bringing up mucus and the soup came with it.
It's pretty common, Pie woke up coughing the other day & vomited up a heap of milk but was fine after & since.

I would just keep an eye on him, see how he goes today. Maybe if he's still vomiting tomorrow or if it's really persisten through teh day today, get him checked out. Whatever the cause, be it a tummy bug or food that was off or a cold, you need to keep an eye on his hydration, make sure he is getting plenty of fluids. If he's lethargic, has no wet nappies or can't keep any fluids down you will need to get him checked out sooner.

Hope he's feeling better soon