The wording is pretty explicit, here:
The thrown property does not turn a melee weapon into a thrown weapon, it mearly allows you to make a ranged attack by throwing it, and, additionally, if it is a melee weapon, you use Str for the attack and damage rolls. This last part is mandatory, unless the weapon has finesse.
Of course, if it is a ranged weapon with the thrown property, you can only use Dex unless it is also a finesse weapon. This is because ranged weapon attacks all use Dex and the finesse property allows you to choose to use Str or Dex with that weapon’s attacks and damage.
What’s my point in bringing all of this up? The point is, there is a clear distinction in the rules between melee weapons with the thrown property and ranged weapons with the thrown property. They function differently.