A transfer is a transfer and to decommit is to decommit.
They are different.
After an NLI contract for an athletic scholarship /financial aid has been signed, the school must release the player or else the player risks needing to sit out a year and possibly losing a year of eligibility.
IMO one of the differences between the two is whether the student started to attend school or received any of the contractual benefits yet.
Also, signing an NLI stops the recruiting process because the student promises to stop communication with other colleges.
"If you change your mind after you sign and want to “decommit” to the college, you risk losing one year of eligibility at your new school, and must sit a year of residence and not compete."
A breakdown of the updated college sports commitment process - and how to stay eligible without the National Letter of Intent.
honestgame.com