Transfer learning in ML refers to the general idea of taking a model trained for one domain and applying it to another. However this article seems to only focus on feature mapping, ie. breaking down images into features using hidden layers of ImageNet models. In this case, the pretrained model is only acting as a feature extractor because it is not trained to maximize the embedded distance between the classes you are trying to differentiate.

Your right the article doesn't do justice to all of the transfer learning techniques. I cut out large portions of the original draft for brevity. Will write a longer post referencing all possible techniques, hopefully it won't turn into a review paper.

Your right about excitement been generated from new techniques in the research community. Also if you look at Prisma, Google photos or any number of applications that have gained mass popularity. They are just implementations of existing networks and techniques. The paper on style transfer made Prisma possible, commercialization usually has been a few steps behind research.

True that most excitement in the field has been in finding new architectures and building general purpose AI. However I would like to point out that people often underestimate potential of transfer learning. We have started solving real problems companies are facing right now because of lack of enough data to be able to train an accurate model themselves.