This guy has insane talent.

I wonder how many he has to scrub because they get off the subway before he can finish.

All wearing masks. Nice. Except for the artist himself?

I totally understand the woman who outright bursts into tears. NYC can be a lonely, alienating place. You close down to live there. If you're friendless and alone, if your entire world is a studio in Brooklyn, if you feel like a spec of nothingness and that your life is stripped of all higher meaning, imagine what it would be like to feel human contact again with a simple act of joy and kindness. For one second, she was a human being again. For one second, she saw the light of man's humanity and empathy towards others. For one second, she mattered.

Simple acts of joy and random act of kindness.

I had to pause the video after that bit. I went to the artist's YT page hoping for a longer cut of that where perhaps she explains her reaction, but it's the exact same clip. So I pondered the possible reasons, and came to the same conclusion you did: she felt invisible / desperately lonely, and this was a rare "someone actually SAW me" moment.

I have a good friend who has been living in NYC for around 20 years, and in the past 18 months he's basically been in isolation due to the pandemic. He seems to be talking about moving back to our home state, seriously, for the first time.

I assume they take them off briefly for the selfies. Masks are likely mandated on the subway.

I was wondering about drying time with the finger painting... might be why there's only one of those (or perhaps the impracticality of wet paints on a moving vehicle).

Please dont overthink this, those techniques take TIME to finish.
People on the subway dont have that much TIME. Also the subway train MOVES. The artist needs a STEADY hand and paper (and good light).

But then again these are PROBABLY the ones out of a HUNDRED where all conditions were FAVORABLE. (just sayin')