The gasoline engine tops out at 70 HP (but you have to be going over 60 MPH to get there). That one's easy for the ad guys to get right, their used to it. The larger electric motor can convert up to 33 kW (44 HP) of electric power to mechanical power (you have to be going over 18 MPH to get this much power conversion). But it doesn't create this power out of thin air, it receives the electric power from both the battery and from the gasoline engine (via the smaller electric motor/generator). Since it receives some of the power from the gasoline engine, this power does not go directly to the wheels, so you must be careful not to add the peak output of the gasoline engine and the electric motor to get total peak output. The battery can contribute at most 21 kW (28 HP) of electric power, so when the larger electric motor is converting 44 HP, at least 44-28 or 16 HP must come from the gasoline engine. The easiest way to get the real peak HP is to add the peak contributions from the gasoline engine and the battery so you get 70 + 28 or 98 HP. The electric motor peak doesn't enter in because its contribution is really coming from the other two. The ad guys really don't get this point.
In the U.S., electric power is usually measured in kW while mechanical power is usually measured in HP. But the two units really are measures of the same physical concept. You can easily convert by multiplying HP by .746 to get kW (or dividing kW by .746 to get HP).