Lenny made a mistake in using the wrong angles when stating that they are right angles. The correct angles should be ∠LMI and ∠LMJ, not ∠MLI and ∠MLJ. Therefore, the correct response is:
"The definition of a perpendicular bisector tells you that ∠LMI and ∠LMJ are right angles, not that ∠MLI and ∠MLJ are right angles."