SC 100HW With Honda 160 cc Engine Binds Up

While mowing the lawn yesterday my mower suddenly stopped. I tried starting again and the starting rope would not move. I checked the oil and it was up to normal level. I then removed the spark plug wire and manually rotated the cutting blade until it rotated normally. Reconnected the spark plug wire and the mower started as usual.
(1) Is this something I should be concerned about?
(2) What do you think may have caused this problem?

Thank you for your responses.

i would pull off the top plastic cover and expose the flywheel and be sure its free of any foreign materials.