Emulators like QEMU are designed to emulate an existing instruction set such as x86, and they also need to emulate a specific memory model, interrupt model, I/O

Emulators like QEMU are designed to emulate an existing instruction set such as x86, and they also need to emulate a specific memory model, interrupt model, I/O subsystem etc. VMs such as in this post are designed without such constraints. Both are designed around the core principle of a "virtual machine" — decode some kind of stream of machine code instructions, execute each instruction, and maintain the stack and memory state along the way — but they target different use cases with different nuances in the implementation.