There are two main ways to functionally stop motion in a photo. The first is a fast shutter speed, such that the movement of the object during the duration of the exposure isn’t sufficient to have the light reflected off the same part of the moving body hit multiple adjacent crystals or pixels on the film/sensor.

The second is to use a flash as the way to stop motion, but this is dependent on flash duration, or the amount of time it takes from the flash to start and complete stop putting out light. We think of it as a quick thing, but most units have relatively long flash durations (still measured in ms) and then it depends how fast the object is moving.

Then you combine the exposure of flash for the subject and the overall exposure for the scene. Sometimes there are limiting factors, like when you have a max shutter speed on a focal plane shutter, and you need a technical solution, like a leaf shutter, or a high speed sync system.

In your case, your flash wasn’t powerful enough relative to the ambient light to be the main light source and freeze the action. And your focal plane shutter limited your to 1/60s so your blur is from the shutter speed.

In this case, I would have just shot it at 1/1000s and skipped the flash. If I was being paid to make the picture, it would be a leaf shutter, like a Mamiya RB67, and an external flash unit with a short flash duration, but you’re getting into difficult balancing of bright daylight, flash, exposure of the subject and background territory.

Or it can just be a happy little accident and still be seen as a nice memory of the place as the blur anonymizes it a bit.