Can happen with breast feeding as well if they aren’t latched properly, it’s happened to my girl a couple times when she’s fallen asleep nursing and just comfort suckled in her sleep so she didn’t have a good latch
She entirely breastfeeds and is 13 months. She had a little blister when she was newborn in the same place from her latch but it looked clearly like a blister. This one i wasn't so sure.
It's a little blister they get from bottle feeding. Completely normal x