Is the stone giant’s 15′ reach with the greatclub an error? [duplicate]

The standard stone giant stat block has a reach of 15′ with its greatclub melee attack. However, I can see no reason from the rules or description for it to be so, instead of the standard 10′ reach of all other huge giant melee weapon attack. Is this a typo that has not yet been caught, or is there some other explanation for this longer-than-usual reach?