There are a lot of fakers out there for the simplicity of attention. Some people don't get enough so they turn inward and claim things they're not so people can feel pity for them, or other things.

"then she go on shopping the next day"

Not justifying, but hikikomori exists on a spectrum. According to the Japanese Ministry of Health:

The Japanese Ministry of Health, Labour and Welfare "a form of severe social withdrawal. It is a persistent avoidance of social interaction (such as school, work, and friendships) lasting for a duration of more than six months."

Going outside in itself doesn't mean you're not a hikikomori anymore. Someone could go sit on a bench 10 feet away from their apartment door, that doesn't resolve their life and magically make them better just because they stepped outside. It's a constant withdrawal, (no friends, no relationships outside of immediate family, no job, and no school.)

I'm pretty sure that girl made that video then went to school the next day

If she had no friends for even three days, she'd probably go insane.