Some human populations "know" how to digest milk, and some don't. Non species-specific. It's a bit of locally acquired "genetic knowledge" as well.
What's surprising here?
What differs is whether we stop digesting milk, not whether we know how in the first place.
All spiders can see eggs in the fangs of their opponents. What differs is whether they react to it.
To say that adult lactose digestion is similar to Portia's egg sac spotting abilities is to say that all spider's have an egg sac spotting gene and it's only expressed in the Portia species in a specific geographical area.
Maybe, but then we have an issue with the rest of spiders. If spiders have an egg sac spotting gene, is it inactive during certain times?
Actually you may be onto something, being able to spot an egg sac would be useful for a male to determine the receptiveness of a female to mating. Maybe the Portia spiders in the specific area have a mutation so they are always looking for egg secs, instead of just when a male is looking for a mate.
So, different populations of same species are expected to have evolved different subtle traits.
I don't think that Portia too carry eggs in their fangs. Nothing points to that as I recall.
I'm trying to say that the development of what almost looks like a learned behavior but is possibly a geographically isolated gene is more surprising than the modification of a gene so that it is expressed past childhood.
We see the latter all the time in other forms if you look at domesticated animals as we have selected for the cute and cuddly traits for adult animals that are normally present in infant forms.
To claim that "that animal is thinking X" you need to discard or at least discuss all possible alternatives. Is very "annoying" when you design a experiment, because maybe you just do not have the money to cover other interpretations, and some kind of experiments have more possibilities to be funded than other.