You don’t have to know Pythagorean geometry to make a perfect square or rectangle.
You just have to be able to measure.
Put a post in the ground.
Tie one end of a length of rope to that post.
Stretch the rope out to its full length.
Walk in perfect circle.
Exactly. They simply observed and measured.
Both diagonals need to be equal. Use a rope to measure. If one diagonal is longer than the other, rotate the side until they are equal. Then you are square.
Knowing a ratio of 3-4-5 sides form a triangle with a right angle is not knowing the full scope of the Pythagorean Theorem. That knowledge comes well before accurate measurement with a protractor, compass, and ruler. It’s also more exact than measuring is.
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You are correct.
A simple rope with knots in it could have produced the results.