I always assumed Bohenny was a slight but typical, change of spelling for Bohenie surely that's more likely than Bohemia?

In a literal sense, maybe, but maybe not in a figurative sense.   Here's a clip from the ever-reliable (*smile*) Wikipedia:

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Bohemianism is the practice of an unconventional lifestyle, often in the company of like-minded people, with few permanent ties, involving musical, artistic, or literary pursuits. In this context, Bohemians may be wanderers, adventurers, or vagabonds.[citation needed]

This use of the word bohemian first appeared in the English language in the nineteenth century

The term Bohemianism emerged in France in the early nineteenth century when artists and creators began to concentrate in the lower-rent, lower class, gypsy neighborhoods. Bohémien was a common term for the Romani people of France, who had reached Western Europe via Bohemia.
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Now, Child's versions are listed from 1792, so it is at least possible that selling them in Bohemia was understood to be analogous to buying something from 'a man in a pub': a sort of no-questions-asked deal. It needs someone much more knowledgable than me to say whether there is any merit in this idea (Malcolm Douglas, RIP: sorely missed)