Unlocking the pixels also requires an internet connection, to determine whether the device has any restrictions on it.
From the grapheneos installation instructions:
"""
On device model variants (SKUs) which support being sold as locked devices by carriers, enabling OEM unlocking requires internet access so that the stock OS can check if the device was sold as locked by a carrier.
"""
From the grapheneos installation instructions: """ On device model variants (SKUs) which support being sold as locked devices by carriers, enabling OEM unlocking requires internet access so that the stock OS can check if the device was sold as locked by a carrier. """
https://grapheneos.org/install/web#enabling-oem-unlocking