Eh, it's hard to say based solely on that video.

I'd say he's about a notch lower than Smart on leaping ability/explosiveness off the jump, and Smart isn't a top-flight athlete in that regard by any means, though he certainly looks pretty decent in the video below.

https://www.youtube.com/watch?v=FuyD3JOwnug

He doesnt get up high but he does cover ground. Some people say he isn't a good athlete because he doesnt explode enough for highlights or use his speed on defense enough. We collectively need to think of this like looking at Devin Booker. Booker was considered a better than expected athlete after his combine and was also called the best shooter of his draft. Murray best Devin Bookers numbers in stats and athletically and he isn't getting the same respect as an athlete and shooter. Booker avg 13.8/2.5/2.6 on 42% shooting (34% from three) this year in the NBA. Booker also had a few 30+ point games as a rookie to boot. If Murray is a better athlete, equal shooter, better ball handler and better rebounder (1 inch shorter in height though) what kind of production just coming in can he put up? Does 16/4/3 on 44% shooting (34% from three) sound reasonable? That is rookie of the year consideration levels in a normal year. Point is Booker looks like he belongs and can be an impact scorer and Murray is on the same curve.  If C's get a better Devin Booker at 3 should any one be disappointed?

Does being able to dunk like that even matter if you don't have the quickness and ball handling ability to get to the hoop in the first place?

He's not a bad athlete. I'd say he's a average to pretty good athlete. So skilled that it doesn't matter.  Probably the same athletic level as Smart although Smart is significantly heavier and stronger.

about average for a guy his size and age(for an nba athlete)

He's a below average athlete for the NBA. He just has an incredibly good shot and balance on his shooting. My worry is that even in the NBA that won't be enough to get his shot off consistently. He seems like a gym rat though so he'll do everything he can to become slightly more explosive.

Or Larry Bird.

3.5/10 at the NBA level.

Coming into the NBA, a significant majority of good NBA shooting guards are more athletic than him. Taking into account the fact that some of his competition is past their athletic prime, he'll be at a slight athletic disadvantage on most nights, but it isn't an insurmountable disadvantage.