My take on quarantine is a bit different from that article in a few points. I do not quarantine any chicks I get in the mail from a major established hatchery. I trust their biosecurity methods to deliver disease and parasite free chicks. I do believe in biosecurity. The only way I bring new birds here is to get chicks from a hatchery or hatch eggs myself.
The source of the birds matters. As the article said a big risk is with animals (all livestock like cattle and horses, cats and dogs form a pet shop or shelter, as well as birds) that have recently been exposed to others like from an auction, swap, or show. If the birds have been kept in a closed flock (where they are not exposed to other new birds) then they have essentially been in quarantine. But this requires a lot of faith that the person keeping them would recognize a disease or a parasite if they saw it plus that they would tell you if they did. There is certainly a risk in this approach. But I'd feel a lot more comfortable with birds from a closed flock than birds form a swap or auction.
What the article did not explain that much is flock immunities, though that is the basis for what they call a canary. Some flocks have developed an immunity to certain diseases or parasites. Coccidiosis is a great example but there are others. They are infected and can give the disease or parasite to other chickens but no matter how long they are quarantined they are highly unlikely to ever show symptoms. It is possible that due to the stress of the move you might see something but the chances of that are so small I would not depend on that at all. That's where putting a sacrificial member of your current flock greatly improves your quarantine, it takes care of the flock immunity issue. It is also possible that your current flock has the flock immunity. If you put a sacrificial bird with the new birds and the new birds get sick then the new birds are not the problem.
Now to your basic question. Parasites or diseases can be spread by the chickens being next to each other, sharing space or eating and drinking from the same source. Insects like mosquitoes can transmit diseases. Some can be carried on the wind. How effective your quarantine is will depend on how you handle these. Housing them side by side across a fence doesn't do much. Keeping them far enough apart so they can't scratch dirt or bedding to each other will help some. Mosquitoes and wind are a lot harder to manage.
I don't know what your facilities look like or what is available to you. I don't know how hard you are willing to work to achieve a good quarantine. Those are the things you are going to have to work out but maybe you have enough of the basics to work with.
Good luck!