The logic is using bazel Runfiles API per Jon's suggestion.
One of the scenarios used by the fuzzing framework is to place the binary and its runfiles into a folder, resulting in a directory layout like this:
[temp dir]
fuzzer
fuzzer.runfiles/
Tested:
bazel test -c opt explorer/fuzzing:explorer_fuzzer
bazel build -c opt explorer/fuzzing:explorer_fuzzer + run the binary from various locations