Shimano Steps ebike performance shows weird assist levels

Shimano EP8 and an Edge 530.

The Garmin unit receives data from the motor and gives me pretty graphs to look at. 

The Motor has 3 levels of assist. Eco, Trail and Boost. When I review the data after a ride, the graph shows the assist level as 1-5 rather than 1-3.

Im confused where the Garmin is getting levels 4 and 5 from as there's only 3 levels on the bike. 

Has anyone come across this before?