The Error: The original phrase "were lies" is grammatically incorrect. "Lies" is a present-tense verb (third-person singular), and it cannot be used with the auxiliary verb "were."
The Correction: To describe something in a state of being in a flat position, we use the verb lie.
Since the sentence uses "were" (past tense auxiliary), we need the present participle (lying) to form the Past Continuous Tense.
Structure: Subject + were + verb-ing (The keys + were + lying).
Confusion Alert (Lie vs. Lay):
Lie: To be in a flat position (Intransitive—doesn't need an object). The keys lie there.
Lay: To put something down (Transitive—needs an object). You lay the keys down.
Because the keys are doing the action themselves, lying is the correct form.