The difference is based on how both directors viewed this character. The original creator who designed the 'dark aesthetic' for him, and the new director, who reinterpreted him entirely.
Nomura's Noctis was a badass who acted cool, and essentially was cool, but didn't feel cool on the inside when push came to shove. He was more emotionally reserved and kept his poker face on, but i doubt there was less emotional stirring in him than what we're seeing here, it would just take more consideration for the player to pick out.
In the 2009 trailer with Stella at the party scene, i was always shocked because you always kind of assumed that Noctis would always be the cool badass guy who never broke from character, but he was very amicable and lighthearted when talking in normal conversation when talking with her, even though he was still reserved to a point.
On the other hand, Tabata's Noctis is more of a teenager in that all of his actions are directly telegraphed to the viewer via him outwardly projecting those feelings, screaming or ranting, or actively showing the viewer his emotions on his sleeve in a far more simple manner. If this was an anime, this is the character people would be complaining about him whining like a little girl throughout these instances.
For me though, again, its just a matter of how the character is interpreted. They are different takes, but i don't think the initial premise of each type of the character is inferior or superior.
I think we've just seen more of him. IMO he's still the somewhat the same as to what Nomura described years ago. http://gematsu.com/2010/08/final-fantasy-versus-xiii-all-the-details-so-far
Everything we've seen him so far in XV has been interacting with the bros. Some of what Nomura said in that interview describes Noctis with his friends such as the calm and confident part. The shy part can been in very small glimpses such as in Brotherhood ep4 where he shys away from talking to the two girls or doesn't talk much to Cindy in the Duscae demo.
We've only seen him interact with Luna as a kid so when he does eventually meet up with her it won't be the same since they haven't seen each other for 12 years. So that version of we see of him in the Stella scene could very well still be there. Just another side of his personality that we haven't seen.
And that's the thing with the Versus stuff. We had very little context on his character besides the scene where he talks with Stella. We all thought he was badass/cool cause of the way he was introduced to us. However, I still think his character hasn't changed much. I can look back at the Stella scene and not feel a disconnect with that Noctis and with the current Noctis.