I think the book has more to it than you are getting from an interview. Also I am not sure what language the interview was in, but English is not Dr. Gonzalez's first language and sometimes he can be hard to understand when he speaks English. The book was translated into English (and perhaps other languages, I do not know) and reads very clearly. It has been revised at least once to reflect current science, and has been recommended by LLL for over a decade. It covers the entire subject of food (including breastmilk) intake by babies and children, what is "normal" gain and growth and what is normal in both nursing and eating habits, what various child feeding guidelines say and how they differ country to country and how they are often based on culture and tradition and not necessarily science, he looks at allergies and how they might be avoided, what nutritional issues might cause poor appetite, when to worry and when not to worry, etc, etc in some detail. It looks at multiple worries at multiple ages and situations. Yes of course a big message of the book is he urges parents to stop trying to "make" children eat and, more to the point, urges doctors to stop scaring parents so they feel the need to do this.
But the problem is much more nuanced than literally forcing children to eat or anything like it. Few parents would do this, but lots of parents feel pressured to somehow get their children eat more and either are miserable because they think they are failing to adequately nourish their children or they are desperate and decide to somehow pressure their children to eat more (but not usually by force feeding.) Spending an entire day making and offering dish after dish to tempt your child is of course not force feeding but it is a sign that there is undue pressure about food intake that you feel and your child possibly feels from you.
It is entirely normal for a child this age to prefer certain textures when eating. If you think your child has some sensory problem causing him to have trouble handling certain textures, maybe it makes sense to see a specialist in that area. But I think that is pretty unlikely to be an issue. I thought the same thing because my son would barely touch solids until he was over 14 months and spit out most textures I gave him. In his case he hated the softer stuff and wanted ONLY firm foods he could pick up and eat with his fingers, but again, not until well after 14 months. I stressed about this for ages even after he started eating and finally found reassurance in My Child Won't Eat. My son is now 10 and has never exhibited any abnormal issues with food or sensory issues. As far as baby refusing harder foods due to having teething pain, maybe that is involved. But then I am confused why there is so much concern? That seems fairly straightforward.
As long as he gets enough of it, probably. But you might need to be sure his iron levels are normal as breastmilk may not provide enough of that at this age. Dr. Gonzalez talks about this (breastmilk as a very completely nutritious food) as well in his book.I wonder if breastmilk still has the ability to provide the bulk of his nutritional need in the second year if I try to up my supply during this time that his gut attempts to heal?