Armstrong recommends installation on installation APA underlayment grade plywood. No guidance is provided for oriented strand board (OSB). Nail pops in newly installed OSB indicates improper nail selection. The nails should be a ring shank 8D nail. I have always used A-CX plywood glued with liquid nails and nailed with 8-D ring shank nails.
The presence of nail pops is an installation defect rather than a manufacturing defect. I would guess the contractor is responsible for repair or replacement. Armstrong has good product warranties and even guarantees against DIY install errors. You might take a look at their web-site and contact them at http://www.armstrongfloors.com/ressheetna/vs_self_install.jsp .