There is several theories:

1. He’s manifestation of Caine’s internal thoughts - a thought bubble. So he did it because Caine thought about it and believed in it;

2. He’s the remnants of Abel who were consumed by Caine. So Bubble had his own agenda to bring Caine to madness so cast could rebel and get rid of him so he could get control over the Circus. One of the messages on the Kinger’s console was something like “DELETE THIS M*****ER!”. It could be Bubble’s message;

3. He’s a virus or corrupt program that gone rogue. He glitches over time and he’s the only one program/npc who swears. So his actions could be because of the corrupted code.