british english - Would the "Cavendish drawl" be considered a dialect?

I was reading the biography Georgiana, by Amanda Foreman, and came across a description of what she calls the Cavendish drawl, an accent of sorts that was spoken by the Cavendish family. One blog refers to it as a patois and wrote that:

the Foreman biography quotes various examples of the phenomenon called variously ‘Cavendish drawl’ and ‘Devonshire drawl’ both of which terms, even taking into account her mention of “bal-cony, con-tem-plate” and “cow-cumber”, are no doubt less appropriate than the third one ‘Cavendish patois’.

He goes on,

In the OED Murray remarked in 1885 “Till c1825 the pronunc. was regularly bælˈkəʊnɪ; but ˈbælkənɪ..., ‘which,’ said Samuel Rogers, ‘makes me sick,’ is now established.” ...
OED dodgily gives the con`template stressing in second place (as an allegedly current usage) even tho retaining Murray’s century-plus-old comment that it “begins to have a flavour of age”.

On cowcumber it gives his 1893 remark that such a pronunciation was “still that recognized by Walker; but Smart 1836 says ‘no well-taught person, except of the old school, now says cow-cumber ... although any other pronunciation ... would have been pedantic some thirty years ago”. Other items of the patois Foreman quotes are yellow, gold and spoil presumably pronounced as /jӕlə, guːld/ and /spaɪl/ and a “baby-talk” style you pronounced with its yod dropped.... Except for this last item, these were all probably merely old-fashioned. For example Wyld's History of Modern Colloquial English (1920/36 p. 239) sed of goold that “It was a very usual though by no means the only pronunciation in the seventeenth and eighteenth centuries among good speakers.”

Whether or not this way of speaking was old-fashioned, it was (according to Foreman) used in the Cavendish household, and was at least partially adopted by people of that social circle. Wikipedia says that a dialect is:

a variety of a language that is a characteristic of a particular group of the language's speakers.[1] The term is applied most often to regional speech patterns, but a dialect may also be defined by other factors, such as social class.

A patois, again per Wikipedia, is:

any language that is considered nonstandard, although the term is not formally defined in linguistics. It can refer to pidgins, creoles, dialects, and other forms of native or local speech

So how would the "Cavendish drawl" be linguistically categorized? Is it a dialect? A cant? Something else?

Answer

What about a minimal dialect:

A dialect spoken by one individual is called an idiolect.
Everyone has small differences between the way they

talk and the way even their family and best friends
talk, creating a minimal dialect.

Source: Sociolinguistics lecture slides