Debian 10 buster / Linux 4.19.0-11-amd64 / Quota version 4.04.
quota -P -s 200
Disk quotas for project #200 (pid 200):
Filesystem space quota limit grace files quota limit grace
/dev/loop1 301M* 200M 250M none 2 0 0
The Hard limit Not effect, can still write in.
Anonymous
As I'm looking at the screenshot, it seems that you're performing the test as root - root (in fact any process with CAP_SYS_RESOURCE capability) is allowed to exceed hardlimit.