Your assumption was a fair one. I used to smoke a pipe but gave it up more than six years ago. I will still have a small cigar perhaps five times a year. I think the nom-de-plume originated at work in the late 60s when it was applied as a nickname to recognise both my pipe-smoking and my known interest in railways, but the exact circumstances are now lost in the mists (smoke?) of time. I do recall that, in that same workplace, my aromatic pipe smoke caused a colleague to enquire 'What is that you're smoking?'. I was busy adding up a column of figures and dismissed him with a rather curt 'That's my business' - to which he immediately responded 'Well, it certainly smells like it!'. Happy days ...