I wonder what the commenter sees wrong in the picture.
The two pieces of angle iron have been welded together into a C-section and bolted to the body of the grinder using the manufacturer-supplied threaded holes normally used for the side handle (you can see the head of the bolt).
He is drilling a hole in another part of the fabricated bracket in order to attach it to something or something to it. Having the grinder in place stops the wings of the C-channel flexing due to downwards pressure of the drill bit and also gives something to hold onto.
About the only thing wrong is that it is not clamped down.