I took his reaction over the neopmorph's death to be more about the progress he felt he was making in connecting with it...not its death necessarily. Sort of like having a computer shut down randomly when you're in the middle of writing something. It's the loss of progress, not death, that made him so angry.
At least that's how I took it. And if he perfected the xeno, it was built to kill and be killed. It was serving its purpose, which is why David wasn't upset over those deaths. He knew he could make thousands more.
That doesn't really make any sense. But then none of it really does. Why be bothered by the loss of the neomorph, which is basically a by-product, and show no concern over the loss of his master creation (twice, as highlighted above)? Why did David let Oram just brush him to one side, when he has vastly superior strength and reflexes? Why blow on the neomorph's nose in the first place? It's not a horse. That makes as much sense as blowing on the nose of a lion. How might that work out I wonder? Why did Oram suddenly then become so monumentally dumb as to follow David anywhere? I don't think these are the questions Ridley Scott meant for me to be thinking about.
I took David letting himself be brushed aside not wanting to show his hand quite yet. And why wouldn't Oram follow him? As far as he knew David was still behaving rationally, and if there were any suspicions, certainly Oram wanted to know what they were up against. He had the gun and David had not attacked him.
Blowing on it...it was experimentation. David using the knowledge he had and seeing if it had any effect on the Neo, which it did. I see David as willing to try anything to learn about the creatures.
But...you didn't like it. Fair enough. It made sense to me at the time as I was carried along with the story. Sometimes I get swept up in what's happening and I don't really question anything as it moves forward. I'll analyze and pick it apart afterward, but in the moment I just like to experience it.