Perhaps it is (or at least was) to some extent regional. Oxford English Dictionary does not have the sense of "trader" that's being discussed here. It does however have "tradesman = A man engaged in a trade or a skilled manual occupation". It also has a second sense for that word: "tradesman = A man engaged in trade or the sale of goods and commodities" and one of the examples for that sense, from 1906, is this sentence:

> ‘Tradesman’, which in the north is used to denote a workman who has learned a trade, while in the south it is made to apply to a man who runs a business.

That was more than a hundred years ago and things may have moved on a bit since then, and in any case that sentence is quoted as an example rather than a claim by the editors of the dictionary, but perhaps despite my current place of residence I'm a northerner at heart?

I mean, one of the most well known sites in the UK for finding people for all kinds of jobs is literally called "TrustATrader.com":

https://www.trustatrader.com/trades

So no, I don't think that's a regional thing.