Enquiry about "GPU-Util" item from nvidia-smi output

I am using Supermicro X10SRA-F mainboard, and obtaining display from the built-in ASPEED Graphics card.
I also have two GTX 1080 Ti graphics cards installed.
The OS is Ubuntu 16.04.2 and NVIDIA-Linux-x86_64-381.22.run driver has been installed.

lspci | grep -i vga
02:00.0 VGA compatible controller: NVIDIA Corporation Device 1b06 (rev a1)
03:00.0 VGA compatible controller: NVIDIA Corporation Device 1b06 (rev a1)
09:00.0 VGA compatible controller: ASPEED Technology, Inc. ASPEED Graphics Famil

I suppose the GPU-Util means the current utilization of GPU which should be 0% for both of the two Nvidia graphics cards, since they are not in use.

But the “nvidia-smi” command shows that one of the two cards is 2% utilized. Why?
Is it right?

±----------------------------------------------------------------------------+
| NVIDIA-SMI 381.22 Driver Version: 381.22 |
|-------------------------------±---------------------±---------------------+
| GPU Name Persistence-M| Bus-Id Disp.A | Volatile Uncorr. ECC |
| Fan Temp Perf Pwr:Usage/Cap| Memory-Usage | GPU-Util Compute M. |
|===============================+======================+======================|
| 0 GeForce GTX 108… Off | 0000:02:00.0 Off | N/A |
| 24% 44C P0 61W / 250W | 0MiB / 11172MiB | 0% Default |
±------------------------------±---------------------±---------------------+
| 1 GeForce GTX 108… Off | 0000:03:00.0 Off | N/A |
| 27% 48C P0 58W / 250W | 0MiB / 11172MiB | 2% Default |
±------------------------------±---------------------±---------------------+

±----------------------------------------------------------------------------+
| Processes: GPU Memory |
| GPU PID Type Process name Usage |
|=============================================================================|
| No running processes found |
±----------------------------------------------------------------------------

The act of running nvidia-smi can generate momentary utilization of the GPU(s)

May I know what"s the meaning of “GPU-Util”? It would be better to show me one example.
Thanks and looking forward to your reply.