This is the digital version of "Flag-jacking" where a traveler pretends to be from another country. In it's offline form it's also usually US citizens pretending to be Canadian.
Unrelated, I once on a trip to the US met a group of motorcyclists on modern bikes and with proper, modern safety gear (at Grand canyon I believe). Having never seen this before in the US (outside sports bikers doing it as much as a clothing statement as for safety) I went over and said hi and said this was the first time I had seen this. "We are Canadians" they laughing replied.
I both cringed and laughed at the same time. Thanks for the (not so pretty) picture in my head!
Never once ran into a fellow American traveler who flag-jacked, although we all would share jokes about doing so, with a wink and a nod. I saw the occasional Canadian flag on a backpack, but from my interactions they were all convincingly Canadian. More often I saw travelers from the world over with flags from all the places they visited on their bags.
I always suspected those Americans who actually flag-jacked were of the breed that visited Western-European capitals via tour-bus, dressed like they were on safari, and loudly compared everything to how it existed "back in the States".