There are many reasons for a person with HD to be angry. A list of those reasons might begin with having HD in one's family, losing a parent to it, and losing the ability to support oneself. The list could include putting one's children at risk for HD, being dependent on others for care, and losing control of one's day-to-day activity. There is, indeed, much reason for anger.
These reasons for frustration ,and anger, coupled with a neurologically based impulse control problem, create a tendency to become angry quickly, giving him a "short fuse". The anger can be extreme and frightening to those who see it. And it may be directed at you!
This is the time to give him space or a "wide berth"; that is, protect yourself and those nearby. Keep well clear of him. Do not attempt to reason, explain or persuade. This may further antagonize him. Try to figure out what triggered this angry outburst so that it can be avoided in the future.
People who watch and wait to intervene learn that people with HD often "cool down" as quickly as they "heat up". When it's over, you need not be surprised if the person apologizes to you, explains that, despite a great effort on his part, he lost control. Accept this most sincere apology.
People with HD certainly have reasons to be depressed, but there may be a physical reason for depression. Depressive moods can be expressed as angry outbursts directed at you.
Keep your perspective, and try to decipher the angry message. Above all, don't take it personally. No matter how it looks, it's probably not intended that way.