The human meat buns were made by Sun Erniang.

Before going to Liangshan, Sun Erniang and Zhang Qing ran a hotel. This hotel was naturally a hotel in name, but inside it was selling human meat buns. They killed the passers-by and made meat buns on the dinner plate. Thinking about this kind of thing today, it makes people feel chills down their spines. It is really terrible, but Sun Erniang can do it very well.

The reason why Sun Erniang makes human meat buns:

It has a lot to do with Sun Erniang’s life experience. In the original work, Sun Erniang’s bun shop belongs to Sun Erniang, not her husband. Zhang Qing's, and this shop was also passed down from the Sun family's ancestors. In other words, it was not Sun Erniang who initiated this practice, but this was the way it was in the family.

It is conceivable that when Sun Erniang was a little girl, she would see her father doing some cruel and bloody things. Maybe she was frightened at first, but she had no way to escape. Being able to watch those people and those things, and be "influenced by what happened" over time, Sun Erniang will naturally no longer think that these things are bad or cruel things.