I can actually believe that the adoption agency didn’t provide baby care classes. Their job is to assess suitability as adoptive parents, and go over any particular issues that may arise due to the baby being removed at birth (attachment issues, potential drug and alcohol exposure, therapeutic parenting techniques, and so on).
Adoption agencies don’t provide basic baby care classes any more than the NHS does to expectant couples. The assumption is you either know, from growing up around babies, or you figure it out yourself as you go.
Framing it as “the foster mum told us what to do” is a clear attempt to frame all their failures around being advised badly by her.