At one point I had 9 Emerald Dwarf Raspboras (unknowingly) in a 7 gallon cube tank. I didn't realize there were that many in there, I thought I only had 2-3 in there, but I also couldn't figure out why my plants were THRIVING. Turns out EDR are incredible at hiding and I dislike them for that. Also they do well with overstocking in a well-planted tank.
I think at one point I also had 6 EDR in there, along with some Heterandria Formosa (3-5 I'm guessing?), and a Dwarf Gourami. They got along fine, and the plants did a little too well.
All I'm saying is that if things are balanced right, overstocking isn't the end of the world. Would I recommend as many fish as are in the original pic? No. But small tanks can support a pretty surprising bioload if managed correctly.