Dipsticks measure protein concentration, not amount. And so if you had a small amount of protein in the urine (which is normal) but your urine is concentrated (as it often is in the morning before you eat), then the dipstick will show protein. But in this example, the dipstick would be over-estimating the protein and giving a false positive. It is of course possible that the dipstick was correct but it needs to be confirmed with a more accurate test like a urine protein or albumin to creatinine ratio.
As for your question about protein in the urine when your kidney function is normal; in fact protein in the urine can precede the loss of kidney function. Therefore, having normal kidney function does mean that you couldn’t have protein in the urine. That said, the amount is very important and needs to be clarified as per my comments above.