The theory is that
-The player did Demon Dodge at the correct moment preceding the .gif, which gives Dante an attack boost
-By switching to Arbiter for the final hit of the slash, slash, pause, slash combo, the player gets the final hit of Arbiter's Trinity Smash, which is actually a triple hit, doing the damage of three Arbiter hits (soll auch noch AoE haben)
-Arbiter is the most powerful weapon in the game
-The player hit multiple enemies with said move
The combination of the above deals a huge amount of damage, and is what lead to the style jump.