> My understanding is that CPU/GPU per application can make only single draw call in sequential manner.

The limitation you're probably thinking of is in the OpenGL drivers/API, not in the GPU driver itself. OpenGL has global (per-application) state that needs to be tracked, so outside of a few special cases like texture uploading you have to only issue OpenGL calls from one thread. If applications use the lower-level Vulkan API, they can use a separate "command queue" for each thread. Both of those are graphics APIs, I'm less familiar with the compute-focused ones but I'm sure they can also process calls from multiple threads.