I could point to any number of insurance companies (some of them very well known) that act the same way. I do not know what type of policy this person had but I am unfamiliar with an uninsured motorist coverage that pays the difference between what the other guy had and what the overall cost was. The uninsured motorist coverage (at least in my state) ONLY covers a specified amount for (usually 5 to 10 thous) property damage. Additional coverage can be purchased for medical costs and again that usually has a limit on it.
Uninsured Motorist coverage (UIM) is normally sold in two forms: UIM Bodily Injury and UIM Property Damage. Some companies offer what is called Combined Single Limit (CSL) where the limit is available for either BI or PD. Limits for UIMBI can be upwards of $1M and more if there is an Umbrella Liability policy which has UIMBI limits available/selected. UIM should always be purchased at the same limit as the Liability coverage you maintain on your policy. Most states do not put small sublimits on UIMBI.