Yes—this can be done in-camera with a slow shutter speed plus flash/strobe. The technique is often called dragging the shutter.

How it works:

• The shutter stays open long enough to record ambient light as motion blur.
• A flash or strobe fires for a very brief duration, which freezes the subject at one instant.
• Because the flash burst is so short, the flash-lit subject can appear sharp while moving elements still leave blur trails from the ambient exposure.

Flash timing matters:

• first-curtain/front sync: flash fires at the start, so the sharp subject appears at the beginning of the motion trail.
• second-curtain/rear sync: flash fires at the end, so the blur trails lead into the sharp subject, which often looks more natural.

To make it work, balance:

• shutter speed and ambient light for the amount of blur
• flash power, aperture, ISO, and flash distance for the sharp frozen part

So no, it does not have to be two merged photos; this is a standard single-exposure flash technique.