"It represents a deity, half bird, half human, probably a Garuda, in a squatting position, holding it sides as if it was shivering with cold (Demam means fever in Bahasa)."
hmmm....may takeaway from the thread i linked you to is that many possibilities exist for the source representation, from wayang characters to gods and ogres. But i am not particularly inclined to look at the source of this form to necessarily be Garuda.