I doubt that the ‘buttresses’ will be supporting the seating and roof of the stadium itself, but they are forming the concourse, and so do service a structural purpose, even if it’s only give the impression that they’re enclosing the space and need to stand up.
The buttresses are almost certainly formed of a steel or concrete frame, with brick surrounds, so the bricks themselves will be cladding, rather than structural, but I have assumed that they will be laid traditionally.
A good indicator of how the bricks will be used is probably the extension to Tate Modern, by the same architects: