[Fizzlemizz]

The first parameter in the payload for UNIT_xxx events is the unit that is the target of the event

local unit , x, x = ...
if unit == "player" then
   -- you started casting, sent the cast, failed at casting, stopped casting or got the job done.
end

In your code, "UNIT_SPELLCAST_SENT is the only event where you check for the unit

local function OnEvent(self, event, ...)
	local unit, arg2, arg3, arg4 = ...
	if unit ~= "player" then
		return
	end
	if event == "zzz"  then
		if arg2 == yyy then
			-- whatever for event zzz
		end
	elseif event == "ddd" then
		if arg3 == nnn then
			-- whatever for event ddd
		end
	end
end