nanda-vrajam gate rame
vasudevo ’ham ity ajño
dutam krsnaya prahinot
Sukadeva Gosvami said: O King, while Lord Balarama was away visiting Nanda’s village of Vraja, the ruler of Karusa, foolishly thinking “I am the Supreme Lord, Vasudeva,” sent a messenger to Lord Krsna.
Since Lord Rama had gone to Nanda-vraja, Paundraka foolishly thought that Lord Krsna would be alone and therefore easy to challenge. Thus he dared to send his crazy message to the Lord.