To explain why Miller cycle is based on Otto cycle, we should first talk about gasoline engine and diesel engine (gasoline engine is similar to Otto cycle and diesel engine is similar to diesel cycle). Gasoline engine has low compression ratio, so its thermal efficiency is low (compared with diesel engine), but because of its high power density and low noise, gasoline engine is often used in automobiles. In order to improve the thermal efficiency of gasoline engine, the intake valve is closed in advance (that is, it becomes Miller cycle), which has the advantage that the expansion ratio becomes larger (greater than the compression ratio, and the compression ratio of Alto cycle is equal to the expansion ratio) and the thermal efficiency is improved.
Therefore, Miller cycle has nothing to do with diesel cycle.
Another Atkinson cycle (the intake valve closes late or the mechanical structure is complicated) is similar to Miller cycle, which also makes the expansion ratio greater than the compression ratio and is improved on the basis of diesel cycle.