As a recent grad I accepted an internship opportunity with a household name major tech company. The program had little to no training or ramp up period, instead I was placed on an active team and expected to immediately begin making contributions. My first meeting with the team was an openly hostile discussion between the senior developers over responsibilities and expectations and that persistent atmosphere of hostility made me very hesitant to participate in meetings. I ended up mostly only communicating with my manager and they had me complete a few small, low priority tasks for the team during the few months I was there. My assigned mentor was busy and the few times I came to them with questions the reply was "I haven't done/used this before, I don't know." As the tasks I was being asked to complete were basic web dev I didn't have too much trouble and used my free time to help other interns, one of which completed half as much work as I did but ended up hired at the company. Nearly two-thirds of people that intern with the program get offers but I did not. I was discouraged enough after the internship that I did not apply or look for SWE roles for nearly a year. Now one of the people I met during my internship has offered to help secure me interviews at the company.
I've been told it is a bad idea to say anything negative about past employment experiences. How do I explain my failure to get an offer and subsequent discouragement without "bad mouthing" the team I worked with or former employer?