Faefolk + Rengar interaction

Hoping for clarification on what I believe was a misplay.

Opponent uses Faefolk to target my Vilemaw, attempting to move him from Battlefield A to Battlefield B.

I indicate I have no response and am ready to move to resolution.

Opponent responds by ambushing Rengar to that battlefield, then conquering it for the 8th and win.

I believe that once he passes priority to me on the Faefolk ability, that he loses all priorities once I indicate I have no response, therefore giving him no windows to Ambush in Rengar.

Is this true?