Definitely ironic.
Many have questioned it.
Detailed explanation here as to why the project (and it is an open source project not a business) uses Pixel as the standard... but it is possible to fork and tailor for other devices if you're keen to map the hardware for that device at own risk.
Almost got there with my Samsung S10, but some stubborn aspects that couldn't be overwritten by flash. So went with the standard.
It's about the sandboxing and about removing the os from 'collaborating' with apps to pipe your information who knows where. You can watch the traffic to verify the difference.
I'm not graphene support or really involved but I do like it enough to use as daily driver for last two years... and run foss/secure apps on top.
https://grapheneos.org/faq#device-support