How does 'rude' mean 'hearty'?

ODO: rude {adjective} = 4. {attributive} {chiefly British} Vigorous or hearty

OED: Etymology: < Anglo-Norman rud, Anglo-Norman and Old French, Middle French rude, Old French (Lyons, rare) ruide (French rude) ... (of a person's body) robust, vigorous, strong (1426) ...

I wish to dig deeper than the definition, which I already understand and so ask NOT about. I heed the Etymological Fallacy. What are right ways of interpreting or rationalizing this meaning, in order to intuit or naturalise it, and to help me remember?
Does this definition 4 (of positive connotation) jar with the negative definitions of 'rude' ?

Just as Etymonline and Wordreference.com don't, OED above only states, but doesn't explain, the definition. Above I excerpted OED's lengthy entry; please advise if I should display more.

Footnote: I first encountered this in 'rude health' here, but please beware that I ask about this definition in general, and NOT only this set phrase.

Solution 1:

My sense of it always has been that "rude" is a word that was used either by nobles or, more likely, the rising bourgeoisie to differentiate their social position from that of the peasant, yeoman farmer, shepherd, etc. If your manners and speech are "rude", it's because you lack refinement (and therefore presumably weren't educated well). A "rude hut" would be a shabby one, but the person who lived there wouldn't describe that way.

But then there's also the romantic (i.e., Romantic) notion of the healthy British countryside, especially as opposed to a smoggy, sooty city. Getting up at dawn and taking in a deep breath of salubrious British country air, as a yeoman would do. So, to me—whatever its age or etymology—the word's uses reflect the contradictions of social change and migration from the countryside to the cities.

I was raised to use "impolite"; I guess some people think that to use "rude", unless referring to a structure or other country craftwork, is hillbilly.

Solution 2:

The story behind the two different meanings has to do with the way the word "rood", was used in Old Norse. It means "red". Eric Rood, or Eric Rude, is Eric-the-Red.

The association with this & other red-haired Viking devils came to mean something like "rough mannered". But in the North, "ruddy" also meant "in good health", because rosy cheeks meant you weren't anemic, and you were getting plenty of fresh air.

First, due to Germanic influences, the word was Healthrud or Healthrude. One sees this construction in Norse names still, for example, "Haugarud."

We use red in different connotations too. Red is for love; red is for Satan.