AITA for telling our manager my coworker was running his side business during work?

My coworker Devin repairs bicycles on weekends. It started as a hobby, then became a small side business with an online booking form and a rented storage unit.

I had no issue with it until customers began coming to our office.

We work at the front desk of a community arts center. Devin arranged for two customers to meet him in the parking lot during his lunch break. Then someone arrived early while he was helping with a class registration. He asked me to say he was “in a meeting” and have the customer wait outside.

I did it once.

After that, Devin began receiving bike-part deliveries at work. He said someone was always at the desk, while packages disappeared from his apartment lobby. The boxes did not block anything, but I became the person signing for them when he was elsewhere.

I told him the side business needed to stay outside our workplace. He agreed and removed the office address from his order account.

Two weeks later, our manager asked why a man had been wheeling a bicycle through the staff entrance. Devin said it belonged to a class participant. I knew that was false. The man was a repair customer whose bike Devin planned to take home after his shift.

Our manager looked at me and asked whether I knew anything about it.

I said yes. I explained the customer visits, deliveries and the earlier request to provide an excuse.

Devin received a formal warning. He has also been told he cannot use the staff storage area for personal property. He thinks I could have answered only the question about the bicycle instead of giving our manager a complete history.

His strongest point is that the side business never delayed my break, lost company money or caused a customer complaint. I was annoyed by the small ways it recruited me, but I had already told him to stop and most of those behaviors had stopped. The bicycle was one final bad decision, not proof that everything continued.

I told the truth because our manager asked directly. I also unloaded every example because I wanted the pattern taken seriously. Devin now speaks to me with rigid politeness and says he knows never to trust me with context again.

AITA for giving the whole history instead of answering narrowly?