It was a highly-touted feature of some of the last MFM/RLL disks
Many thanks for taking me back to my first 30MB 5.25in RLL hard disk, then a pair of 3.5in 20MB Lapine Titans.
but does not put it in parking mode
If I have any doubts after closing an external 3.5" or 2.5" disk with "Safely Remove Hardware", I gently touch the USB housing and see if I can still feel the platters spinning. This is much easier on 3.5in drives. Better still, shut down the whole computer before disconnecting the USB drive. Even then, if the drive has its own external +5V or +12V power supply, there's still a chance the heads might not be parked.
Did this event cause damage to the HDD within it?
Instead of theorizing about possible damage, why not subject the drive to a long S.M.A.R.T. scan? Thinking about it until you're blue in the face won't prove anything.
Download an evaluation copy of Hard Disk Sentinel and run a non-destructive "Read test". This can take several hours to complete on a high capacity disk, or even longer if there are faults.
If the scan result comes back like this, with loads of yellow and red blocks, your drive is toast.
Note the elapsed time of 10 hours 10 minutes for this test on a badly damaged 74GB hard disk.
Of course your drive could drop dead tomorrow, even if it's 100% "healthy" today. Make backups.
When travelling, I take a few Crucial X6 portable SSDs, instead of 4TB hard disks. No more head crash worries.
I've seen sights such as this when pulling old hard drives apart, so who knows, perhaps you have damaged your hard disk with that slight knock.
😡