I don't believe that Apple did not know about these initiatives before committing to building Metal. Apple was using the OpenGL graphics API (governed by the Khronos group) and AMD GPUs exclusively around this time period.
Vulkan was created from the Mantle API that AMD donated to the Khronos group. Mantle exist 2 years prior to any mentions of Metal. As a member of the Khronos group and a very important partner of AMD they would surely have information on what these groups thought the future would be of graphics-APIs.
I believe that Apple had other reasons for choosing to build Metal. But I'm afraid it will be hard to figure out what they were.
Note also that Apple is also in the highest tiers of members of the Khronos group. (see: https://www.khronos.org/members/list).
Vulkan was created from the Mantle API that AMD donated to the Khronos group. Mantle exist 2 years prior to any mentions of Metal. As a member of the Khronos group and a very important partner of AMD they would surely have information on what these groups thought the future would be of graphics-APIs.
I believe that Apple had other reasons for choosing to build Metal. But I'm afraid it will be hard to figure out what they were.