That is the real difference. I explained it.
To simplify it further would run perilously close to sarcasm or parody, but here goes.
Spontaneous generation: Not first life. Babies made from different kinds of stuff. No mommys or daddys. Babies just mini versions of big ones. Babies all creatures already seen in nature.
Abiogenesis: First life. Very simple. Not baby, just chemistry that copies self good, is stable, sealed from environment, responds to stuff. Made from long chains of chemicals. Is last part of long, natural process with non life long chains of chemicals becoming better at copying. Is start of new, long natural processe.