that they have infant forms (that appear to have external gills like salamanders)
that they rely on water for their life cycle to complete
that, related to #3, they like chomping on snowballs
that they’re neutral and even friendly when not dehydrated like a frog in summer
In addition to the points in the graphic:
Flat faces with the eyes at the front, like many amphibians
smooth skin
mouth that looks tiny until opened (have you seen an axolotl or caecilian with its mouth open?)
fireballs may be analogous to skin and saliva-based weapons in amphibians
has zero mercy
cannot aim at all
makes sounds quite like the axolotl when you think about it
operates on 1.5-2 brain cells at all times
… We may be able to conclude that ghasts are amphibians.
If we look at this phylogenetically, then we may be able to speculate that ghasts are highly derived (specialized) temnospondyls, which are huge prehistoric amphibians who were like 25% mouth.