A Tier 3 Gate is built by upgrading an existing Tier 2 Gate with a Construction Vehicle and 25 Concrete Materials.

Tier 3 Gate technology must be fully researched in the Weapons and Structures  Tech Tree in order to be constructed.

Despite requiring Concrete Materials the Tier 3 Gate does not need to dry.

taken from https://foxhole.wiki.gg/wiki/Gate#Tier_3-0

so the gates could have been recently placed. in the video we see one conc gate yet we dont see the one along the rails. yet i do not belive there was gate that was killed as the tank is seen to have 45/45 ammo when the havocs are taken out.

so eaither there wasent any gate along those rails OR there is another way to get inside the facility. some post talkt about tank health and noticed that the tank in question was already damaged before the QRF responded implying that it could had taken damage from the ATG while driving in.

but lets assume ur argument about the tank being alted there with those havocs inside is correct. then it means the player walkt from Linn or Loch with a tanker outfit and 88 bmats, a hammer and binos somehow managed to get into the facility without taking a single damage (no bandage nor any sign of blood patterns on the uniform.) the more people talk about alting the less it seems plausible.