The epicenter is the surface location of the focus, which is the spot on the fault plane where the propagation of the slip begins.

It is the slip direction that will affect the seafloor in a way that produces a tsunammi. If the fault moves sideways, then that is strike slip, and doesn't produce any significant change to the sea floor in the vertical direction. If the fault moves up and down that is known as dip-slip, and may result in a big move of the seafloor (but only if the slipping of the fault reaches the surface) which then would result in a displacement of the water column as well.

Not knowing enough about the event (I've not examined the USGS data), I'd guess that it mostly strike slip movement or didn't reach the surface (ocean floor) in any significant way.