Red Bull team chief said Max Verstappen "got Tsunoda'd" on Saturday after he was forced to settle for third on the grid after qualifying for the Mexico Grand Prix.
World championship leader Verstappen was trying to cut into the pole position pace of Mercedes' Valtteri Bottas when he attempted one last flying lap.
But the Dutchman was distracted by seeing teammate Sergio Perez and the AlphaTauri of Japan's Yuki Tsunoda run wide off track ahead of him.
Horner said Tsunoda, who had appeared to run wide to give drivers behind him more space after abandoning his own lap, was at fault for Verstappen ending up on the second row behind Bottas and title rival Lewis Hamilton.
"I think we got Tsunoda'd," Horner told Sky Sports F1.
"Both drivers were up on their last lap. Max was up two-and-a-half tenths, I think Checo (Perez) was just under two-tenths up.
"I don't understand why he was just cruising around at that part of the circuit.
"It's disappointing because it affected both of the drivers because they're both pretty annoyed."
Tsunoda had been eighth fastest in qualifying but will start Sunday's race from the back of the grid for changing engine parts on his car.