A. Yes, it could be, but usually yellow liquid is made only of gastric secretions.
Withhold food for the next 8-12 hours and then start feeding him again with some boiled chicken and rice every 4-6 hours in small portions for 48hrs.
If the signs persists or you notice any other sign such as more vomiting, diarrhea, lethargy, inappetence then I would recommend to take him to your veterinarian for a check up and appropriate treatment.
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