I don't know all the background or laws. Just the fact that the female boarder guard appeared to be throwing her weight around in front of the trainee she was showing the ropes to.
I once crossed the boarder in Prince Rupert into Canada after taking the ferry down from KTN. I was on a touring motorcycle loaded for a cross country trip to the east coast. I had a new front and rear tire strapped to my bike and an appointment to have them changed at a private MC repair shop in Calgary. My tires were down to around a 1,000 miles of tread left and the tires it used were rare sizes so I brought my own. Woman working the crossing went through the usual questions and then settled on the tires on the bike like I was trying to import a semi trailer load to undercut buying them in Canada. We went round and round as to why I was bringing tires into Canada, over and over and over with different angles of questions trying to trip me up. After 10-15 mins she gave up and let me in the country.
I worked 20 years in law enforcement in Alaska. Every time I entered Canada the question of employment came up. Police dept. Where is your gun? Don't have one with me. Where is your gun? Don't have one, Where is your gun. Round and round we would go till they got tired of asking.
I used to carry a 7mm Mouser rifle with me when I transited Canada before it got so complicated with fees and permits. I crossed once from WA into BC. Guy at the crossing gate asked the usual quesitons and about firearms. I delcaired my unloaded rifle behind the trucks front seat. He joted a note indicated I had declaired a firearm and sent me to their office to chat with the office folks and be inspected. I went in, waited in two short lines and was told to return to my truck and await inspection. A short time later a kid came out and inspected the rear bed contents. Then he moved to the cab. Looking under the dash, under the bench seat and then he folded the front seat forward and nearly jumped out of his boots backwards. "THERE IS A RIFLE IN HERE" Yeah, what's your point? was my response. He was holding the piece of paper I gave him from the initial crossing noting that I claimed having a 7 mm rifle in the truck. I said if you look at the paper I gave you it says I declared the rifle back at the initial contact. He then looked at it and stuttered be on your way... I managed to keep a straight face till I was on my way and out of earshot range. Cracked me up. Still does.
After crossing the boarder dozens of times I've always found it harder to get back in the US then into Canada. Except at the smaller crossing points. When we crossed back into the Yukon on the Top of the World Hwy in 2016 we sat and chatted with the boarder guard for 10-15 mins. I asked if they heat with American firewood and a few other questions. Sat and chatted with a US boarder agent between Haines and Haines Jct one time about motorcycles. I was on one of mine. Both times there was no one waiting behind me so we just sat and chatted about this and that.