I know nothing of the specific border crossing the OP referred to but I do know what happened to me at the crossing between Waterton and Glacier NP.
There's a pretty stout climb up to the border from Canada. It was a gray,cool day and it started raining about 10% into the climb. By the time I got to the top I was soaked thru and it was 15° colder then it was at the bottom and I pull in behind the two RV's in front of me. As I'm standing there, pretty soon I'm freezing, and I see at the station there is an overhang and a bench and I think (pretty naively) I'm going to wait my turn over there out of the rain and put some dry clothes on. When the border guy sees what I've done he FREAKS OUT, think about a drill sergeant at marine boot camp dealing with a fresh recruit and you got the picture. And then when I find it kind of funny that he's so far over the top, then he really goes ape sh*t.
To be clear, if I broke with the way things were supposed to be done and he turned to me and said "you cannot be there, you need to get back in line" in an all business way, I would not have taken any offense and would have done what I was told w/o complaint.
This guy was so over the top that the RV who was in front of me pulled over ahead and volunteered his phone # that if I wanted to report this guy that he would be happy to talk to anyone who looked into it.
The bottom line, I know from personal experience that the idea that every single member of the border patrol acts in a professional manner is BS.