S.H.
Well, he is making a 'game' of feeding the dog.
Its a GAME, with the DOG.
I therefore think, that eating has become another kind of activity for him... its not the food, it's the dog & him kind of thing now.
So, feed him elsewhere, without the dog.
Or, if he splats food on the ground, have him help you clean it up. Not in a stern way... but just so he understands, per his age... that food does not belong on the ground.
ALSO though, at this age, they do this... they are getting more independent. It will pass.
Or, when he does that... then just keep calm, take the food away... and stop. Let him sit in the high-chair (if that is where he eats), and then open a magazine and make like you are reading it. Then, after a minute ask nicely "are you ready to eat? Yum!" Then try again. Without the dog. AND, use a plastic floor cover/mat for the kitchen floor for easy clean up. If he splats food on the ground again... say "Wow, its so great I have a mat for the floor so I can clean it up so well, come and help Mommy..."
Or you just take him out of the high-chair... and feed him again later. Maybe he is just not hungry either. This also happens. Some kids won't eat just because the clock says so... they only eat when they are hungry.
Lots of food/eating phases will come up... at different ages.
All the best,
Susan