By that photo alone, no - but you say "4-5 months in this photo" so how old is the horse now and do you have more current photos or photos from other angles?
Being that he's dark and not parallel to the camera its hard to tell. He doesn't scream dwarf to me but there are a lot of minimal dwarfs with only a few small characteristics that are hard to see unless you know to look for them. Is his head more bulbous than 'normal?' Does he have an underbite? Abnormally short neck, large head, or roached back?
I think he might be. Still hard to tell. I'm looking at his neck and head and then the back.
If him being a dwarf is a deciding factor on not getting him, there is one down the road from me that is about a gazillion years old. I don't think he's ever had any issues. He's very arthritic now...
If I get some better pictures I will definitely post them.
I'm not against dwarfs per se, I just know they can have a lot of medical issues and I would want to be able to provide him with the best life possible.
I also have had a lot of heartbreak within the past year (I lost 2 of my dogs 3 months apart to cancer), so I'm just a bit leery.
That being said, if he is a dwarf he looks to be a minimal one compared to other photos I've seen on the internet.
Thanks for posting the link, it's good to see one that's had a nice long life!