The reason that some people say this is because the Lt. Governor has a great deal of power with respect to the legislative branch of the state government. The Lt. Governor does not have more power than the Governor when it comes to the excutive branch, but does have more power with regard to the legislative branch.
The reason for this is that the Lt. Governor has the right to appoint the members of the legislative committees in the state Senate. This is a function that is usually given to the leaders of the parties in the houses of a legislature. In addition, the Lt. Governor even has the right to assign bills to the various committees. This kind of power goes well beyond the power wielded by most governors in other states, let alone Lt. Governors. Finally, the Lt. Governor serves as the chair of the Legislative Budget Board. These are very significant powers and they help to explain why it might be said that the Lt. Governor has more power than the Governor.