Bringing this thread back, because I've been thinking about it recently.
The Art of Tea issue 10 claims it comes from the Fuzhou dialect, and says that it's lap / le (for pine) and sang / xūn (熏) for smoke. However, from asking around, so far, 松 is the only word for pine I can find - I'm not sure if there's another word that only exists in local dialect, or an antiquated word for pine. I think the suggestion that it's Fuzhou dialect (rather than the dialect in the production area) is what they're implying too, presumably because the tea was exported from there.
The article also mentions that the original categories were 正山 (zhēngshān) and 外山 (waìshān), I think implying outside the scenic area, not just 'outer mountain'. From the article:
Art of Tea, Issue 10, p 8 wrote:
Later, teas were classified Real Mountain Zhengshan and Outer Mountain Waishan, in order to distinguish between local and foreign teas.
The original production area of Zhengshan Souchong [read xiaozhong] is Tongmu village, located in Xingcun Chong'An County, Fujian province, principally in the area of the nature reserve, whereas Waishan Souchang, also known as Fake Souchong, refers to the teas grown in Jiangxi, Zhenghe in northern Fujian and Tanyang, etc.
(The article gives all these names in pinyin, with no characters or diacritics)
Usually in modern usage, people seem to specify when zhengshan xiaozhong is the smoked variety.
In any event, it's clear that the Wikipedia suggestion that 拉普山 is anything more than an approximation of the phonetic sound is incorrect. If we can ever figure out for sure where the name comes from, I'll try to update the Wikipedia page.
The article also discusses the traditional production methods (involving a multi-story traditional building (qinglou) in which the same fire passes through multiple stories, and is used for different steps in the process. According to the article's author, the dried longyan aroma should persist beyond the first few infusions.