I've seen that happen often, even from resting the fore stock at different positions. Why he positioned the barrel on the rest is beyond me. :-?
He also violated one of the basic concepts used for attaining repeatability, aka accuracy. He changed an influencing factor, in this case the position of the gun on the rest.
The following is not meant to be demeaning of others but the truth is there are a substantial number of Bench Huggers that sit on their backsides and never standup and shoot. At some point one needs to shoot from field positions to ascertain capability of the firearm, ammunition, and last but least the shooter themselves. You can't buy $$$$$ competency ,but you can earn it by getting of your rear end!
I first decide what distances I'll be using the rifle. Based on that I select a zero distance which takes into consideration sight over bore and muzzle velocity. Once that is settled I head to the range. I'll pick a rock or clump of weed on a dirt bank, then fire #1 and watch for the dirt splat. Adjust scope accordingly. Next I'll fire #2 at paper. Adjust accordingly. Then I'll fire #3,#4,#5 for a group. Adjust accordingly. #6 will be on the money.
Some may wonder why I first shoot at a rock on a dirt bank. It allows me to be reasonably assured that my second shot will be on paper rather than the hunter who blows through a box of 7mm mag and curses that he's not on paper yet. Some guys use laser boresighters and other methods of looking down the bore.
Books can be written on zeroing rifles and optics. When testing a rifle and optic accuracy, the goal is to take the shooter out of the equation. Using a good bench rest helps do that.
Any slight pressure on the barrel can change harmonics and accuracy. Yes, the rifle should always be rested on the forearm. Rifles with two part stocks like lever-actions, pump-actions, semi-autos, and single shots are usually not target rifles because the forearm attaches to the barrel and presses differently on the barrel and changes the point of impact. They are great for hunting accuracy at closer range. A five inch group at 100 yards is still minute of deer heart.
Your hand or fingers should never touch the barrel. I recommend a shooter place the arm and hand usually holding the forearm flat on the table for support. A thumb on top of the barrel can change the barrel harmonics and therefore the point of impact.
Ideally, the barrel should be free-floated. Any barrel heats up with consecutive shots and will warp. If the forearm is touching the barrel when cold, it will amplify the movement when hot.
When hunting, everyone ignores all of this and it usually doesn't matter under 200 yards.
I could write pages on internal and external ballistics and how it equates to downrange accuracy as well as optics mounting but I won't. Suffice to say that I can make just about quality rifle shoot sub MOA at 250 yards. Do it all the time. Probably why I get various rifles to accurize.