The smaller red numbers are your other damage sources. Tell Garuda to attack something and watch her numbers. Usually at end game its ~200 a hit, this way you can figure out what she does and when her numbers appear. Then throw some DoTs and you'll be able to tell which of the smaller sets of numbers are your dots and which are Garuda.

My only confusion in tracking my damage is that sometimes I have a 4th red number showing and I don't know if it's just other people's DoTs also being red or what. I had assumed all party member damage was purple and I have no idea where a 4th comes from. Pretty sure Garuda doesn't have an auto-attack or anything