Maybe not surprising biologically, considering the role of nutrition as a limiting factor on human (and most organisms) population. Say an ancient culture developed a lifestyle heavily fishing relient. If the resources (fish) were plentiful, it's not hard to imagine fish becoming a staple diet fast and subsequent adaptations to the nutritional pros and cons emerging within just a few generations.
OTOH, milk requires domestication of mammals. For milk to be a staple (as it is among many existing pastoralist cultures), processing and preservation techniques (yoghurt, cheese, etc) need to be developed. It's (IMO) a pretty complex assortment of dependant cultural and biological adaptations in both humans and animals.
Genetic evidence like this suggests that the adaptations spread fast. It also suggests a substantial role played by pastoralist cultures in neolithic and bronze age prehistory.
Neolithic history is tends to emphasize grain agriculture. These people left more artifacts. They left large settlements (eg Jericho) for us to dig up. They became urban "civilizations." Common, orthodox interpretation (eg the common marxist narrative) focuses on these a lot. Complex relationships between economics & social structure are inferred. etc.
Pastoralism gets a lot less attention. They left few artifacts, fewer settlements. They weren't urban, making them less interesting to most 19th and 20th century historians. Yet, we have lots of evidence that they were both many and significant.
Some of the earliest histories we have (Sumerian, 1st Dynasty Egyptian) suggests all sorts of contact, cultural exchange and conflict with large populations of pastoralists. Ancient historians attributed many innovations in weapons (eg chariots, compound bows) and other technological advancements (eg wheels) to pastoralist cultures.
While speculative, I'd also suggest that the earliest "nations" may have been pastoralists in the Yuval Noah Harari sense of the term. This also makes them the first civilizations in the same sense. They were also likely to have been innovators and originators of long distance trade and communication.
None of that is proved by the spread of lactose tolerance, but it does suggest that pastoralism was a very significant lifestyle in the lead up to pre classical cultures.