If you look at the trailer at 1:33, the vault opens and your view is from inside the vault looking out. The vault is pressurized as it states on the vault door in the trailer. When the door is opening, you can see black hoses connecting to the side of the vault entrance located on the interior and exterior of the vault. Also looking out of the vault, you can see a fenced platform and and a very bright light. This plus the warnings on the door makes me think the vault was sealed from the outside. This is also why I think you see the vertibird flying to the vault, just part of the crew preparing the vault to be sealed.

I don't believe so, I would imagine some prep would need to be done, but I don't think there is a vault out there that would allow for enough outside manipulation as you are suggesting here. There would be an access panel of course, but beyond that I do not think so. I have another look and see if I can align some things your talking about.

Maybe they sealed it because they were experimenting with something maybe it has got to do with the protagonist.

I know this is conjecture but I believe the vault was sealed from the outside and had to be opened from the outside...initially. Someone got into the vault causing the MC to have to leave.

When the Vault 111 door opens it switches to the interior view of the same control room that is in every Bethesda Fallout Vault, so access to and from the actual vault seems to be the same as previous vaults, the only difference is the access shaft. I assume there would be platforms, stairs and lifts in the shaft since it would have to be designed to take a sudden influx of people going into the vault in a small space of time.

All vaults can be opened and closed from the outside.

Your not looking into the control room, your looking out of the vault when the doors open. What you are seeing is just outside the vault...not inside. Also on the surface, where you find people standing to get into the vault you can see, what i think is two computer monitors similar to what you find in FO2 at the Sierra Army Depot, Skynet level. Also next to the surface entrance is a metal handle in the prewar depiction of the vault that is replaced by a red, round shut-off valve with the post war depiction.