It’s likely they just weren’t grown in. I work in produce and the last few times we had issues with E.coli in Romain lettuce (not us specifically, I mean the US in general) we were told that having washed the lettuce or not did not matter. As the ground itself was contaminated before the plants started growing. To note, you also likely washed your produce far better than the average person. You would be amazed at the amount of customers that don’t know that they should wash stuff thoroughly.