The dictionary term of an alumnus is someone who was a student. You do not have to be a graduate to be considered an alumnus by dictionary standards. I've attached a link so that you don't have to use a search engine. You're welcome, by the way.
With regards to someone being officially recognized by an institution as being as part of the alumnus roster, that's up to the individual institution, but it doesn't change the fact that someone who was a student at a given institution at one time or another, is technically considered an alum.
Just to educate you, Jerome Bettis has always been considered as a Notre Dame alum to just about everyone here, even though he didn't graduate from there until very recently. Or, by your own definition, did you not consider him an alum during that time span?
You can't have it both ways.
On another note, you should enroll in some anger management classes, since you seem to be quite triggered by several people's posts. Either that, or do yourself a favor, and use the "ignore" feature built into the bulletin board software.
Link: https://www.collinsdictionary.com/us/dictionary/english/alumnus