What does this traffic sign combination indicate?

You answered correctly. The top triangular sign with the exclamation mark is a general warning sign, indicating danger ahead. The additional sign below it shows a horse and carriage, meaning the warning specifically relates to horse-drawn vehicles.

In German traffic rules, this combination alerts drivers to be cautious because there may be horse-drawn carriages on or near the road. It does not mean that these carriages have priority or that they are prohibited from passing. You must slow down and be prepared for possible unexpected situations involving horse-drawn vehicles, which might be slower or behave differently from motorized traffic.

Remember, warning signs like this are meant to increase your attention and caution in potentially hazardous areas.