Granted, I don't have an OED in front of me, but Merriam-Websters (the American equivalent) defines art as:
Main Entry: art Pronunciation: 'ärt Function: noun Etymology: Middle English, from Old French, from Latin art-, ars -- more at ARM Date: 13th century
1 : skill acquired by experience, study, or observation <the art of making friends> 2 a : a branch of learning: (1) : one of the humanities (2) plural : LIBERAL ARTS b archaic : LEARNING, SCHOLARSHIP 3 : an occupation requiring knowledge or skill <the art of organ building> 4 a : the conscious use of skill and creative imagination especially in the production of aesthetic objects; also : works so produced b (1) : FINE ARTS (2) : one of the fine arts (3) : a graphic art 5 a archaic : a skillful plan b : the quality or state of being artful 6 : decorative or illustrative elements in printed matter synonyms ART, SKILL, CUNNING, ARTIFICE, CRAFT mean the faculty of executing well what one has devised.
ART implies a personal, unanalyzable creative power <the art of choosing the right word>.
SKILL stresses technical knowledge and proficiency <the skill of a glassblower>.
CUNNING suggests ingenuity and subtlety in devising, inventing, or executing <a mystery plotted with great cunning>.
ARTIFICE suggests technical skill especially in imitating things in nature <believed realism in film could be achieved only by artifice>.
CRAFT may imply expertness in workmanship <the craft of a master goldsmith>.
Granted ... most high-end framebuilders are craftsmen ... but some are indeed artists ... having an idea on how the lug should be shaped to empashise its inherent beauty is an art.
To me, there is no difference between a sculptor and a framebuilder ... except that a framebuilders art is functional as well as aesthetic.