We don't know the intelligence of this species. We don't know at what point during evolution our species neared it's current intelligence level.
It could be that 10-20k years ago there was an intelligence breakthrough in our species.
But your suspicions do not have to inform you. You can look at science and evidence critically and skeptically, and your intuitions will be moot.
Science has several ways to date specimens, and they are all backed by the same science that "suspiciously" lead to your car's combustion engine and your microprocessor in your phone and PC.
So your "suspicions" are neither here nor there.
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