Ear infection but no signs of one

I took my daughter to the doctor today after a week and a half of congestion. The last couple nights she has been coughing when she sleeps. I chalked it up to just being a cold. She has not acted sick at all, that’s why I wasn’t so concerned about getting her in to the doctor right away. But they told me she has an ear infection in one ear and a bunch of drainage. Has anyone’s baby/toddler ever had an ear infection but really no symptoms of one? It really surprised me for some reason. This is her first time being sick at 16 months old.