Whatever the reason for not asking that question, it would be a terrible question to ask an interviewee in that situation. "Did you
actually graduate from this place?" It would be the equivalent of asking "did you lie on your CV?" If I wrote a CV and they began asking me questions that were answered by my CV, I would read that as skepticism. Conversely, perhaps the interviewers are so good that they only ask questions where they already know the answers, in that regard.
Neither of you have mentioned the qualifications of the jobs you sought. Perhaps those companies did not require or factor-in the degrees of candidates. Perhaps they can open up LinkedIn and see whether or not you graduated. Perhaps they just called their sorority sister at the Registrar for an informal reminiscence about the weather in 2021.
I can understand if you want to put the year-range that you attended college. Perhaps you want to prove you graduated in 4 years, rather than taking 6. There are more people who are unwilling to put any year at all to their education, lest someone figure out that they are over 40.
The bottom line is that if you ask 5 people about résumé building and job interviews, you'll hear 6 opinions on what is right, what is wrong, what is legal, etc. There is plenty of bad advice, and narrow opinions, mine included.