Warwick can´t passively blood hunt targets that are marked by Garen's Passive

Just played a game as Warwick on my LAN account. Whenever the opposite team's Riven would get low on health my w's passive would not activate on her. I noticed she was marked by Garen's justice passive whenever this occured (She had the sword thing icon from Garen on top of herself). I assume this has to do with both passives being marked as the same item, and Garen's having priority over ww because his was placed first? I'm just guessing on this tho.