I believe only certain versions and on certain architectures is seL4 verified for. There are no bugs found at the C source code level for these builds of seL4.
This issue appears to have affected all architectures. This issue was present in the specification against which seL4 was verified. You can say that there are no bugs by virtue of it following the specification, but if the specification was wrong and in this case it was, then were there really no bugs?
Even if it's not exactly seL4, there's good value in taking inspiration for design elements. It would still be a lot more robust than commodity operating systems.