Since there is zero evidence of any comet having water on it this should not be a surprise. It's like every scientist just glommed on to what they learned in grade school: comets are dirty snowballs, or icy dirt balls. Ever comet visited by spacecraft has looked exactly like an asteroid. Sample returns do not bring water back.
Before everybody piles on with "comet halos are water!" Realize that comet halos are actually made up of dust and OH ions. It is an unproven assumption that the OH comes from water being ionized by sunlight. (Which by the way is not powerful enough to do anything at the orbit of Jupiter where many comets develop their tails.)
But, it's fun to watch scientists be astonished every time there is evidence that comets are asteroids.