Um, I'm sure its cosmetic and has to do with the custom pants script in the repo and things like

./pants

and CWD and things like the now-gone:

$ git diff -U1 2f520bab^! -- build-support/pants_venv 
diff --git a/build-support/pants_venv b/build-support/pants_venv
index 8594030..09691bc 100755
--- a/build-support/pants_venv
+++ b/build-support/pants_venv
@@ -4,3 +4,3 @@
 
-REPO_ROOT=$(cd $(dirname "${BASH_SOURCE[0]}") && cd "$(git rev-parse --show-toplevel)" && pwd)
+REPO_ROOT=$(cd $(dirname "${BASH_SOURCE[0]}") && cd .. && pwd -P)
 source ${REPO_ROOT}/build-support/common.sh