So, the question remains... What other pipework did he do in the loft? And how did he do that?
If it's just that connection, and he works for a "firm" (ie: he's not SE) then I'd be suspecting company policy of no soldering in lofts and he didn't have any compression fittings on board.
Or just laziness, if you specifically asked about copper... Otherwise his decision, but should be clipped and lagged as best practice.
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