That's not how that GPL works. To be precise, although there might be a (very small) chance that a court has found or will find that software running in user space is a derived work of the kernel, that finding would not apply to Linux's user space because Linus declared (in the 1990s) that the conditions of Linux's license do not apply to user space.
Tivo was one of the first owners of proprietary software to test this area of the law: their devices ran Linux, but they never had to publish the source code for the software on their devices that ran in user space.
The distributors of RemixOS would have to publish the source code to any changes they make to the kernel itself, but someone else in the comments says they have made none.
"The Android Open Source Project uses a few open source initiative approved open source licenses for our software"
Android is based on a fork of the Linux kernel which is GNU GPL v2. RemixOS should release their code, it contains several GNU GPL parts.