I would have thought it is very rare for BG to drop that far in 10 minutes unless you are exercising hard with lots of insulin on board.
In my experience, it is more likely that I have some sugar residue on my fingers when I took the earlier/higher reading.
This may be because I have been in the kitchen or it could be something which appears unrelated to food such as newspaper print.
By the way, you ask if this means you took too much insulin but your profile says you don't have diabetes. Does your profile need updating? Or are you just asking out of interest?