No, and he and 'Dave' look about the same size in all the photos we have of 'Dave and Julie' alongside the Walkers. Certainly Dave isn't the giant 'man-mountain' she represents him as, unless the supposedly fragile and emaciated TW is himself a fair-sized, well-fleshed Alp.
@MulberryBrandy, it's less Moth's memory or inability to read his student notes -- that's the earlier Heartbreaking Development that supposedly means he can no longer remember key bits of the SWCP (hardly surprisingly, as they didn't really walk it) which prompts her to start writing TSP as an aide-memoire.
In the timeline of TWS, fictional though it is, he's finished his degree more than a year earlier, the Big Issue piece has come out, TSP has been published and been a huge success, BC has been in touch, they've moved to Haye Farm and miraculously brought it back to life (and have a conversation about the costs of stocking a farm and what they did on Moth's 40th in which he demonstrates apparent total recall), and Moth says he doesn't want to run Haye Farm not because he's totally workshy or dying, but because he wants to go on Raynor's book tours with her.
In fact, weirdly, given the whole might Moth need to be medivacuated from the Icelandic trail, or, even worse 'Will he have to confess incapacity, use walking poles and have Dave carry his rucksack, thereby meaning his fragile masculinity is permanently compromised?', Moth is apparently perfectly well before they leave, and the walk is not some desperate attempt to save his life again, but a deeply ordinary desire to go on holiday with friends...
I'd forgotten what a deeply odd patchwork of a book TWS is.
It's so obviously cobbled together in the spirit of 'I desperately need to write a sequel to capitalise on the success of TSP, but have literally nothing to say because our personae are fictional, Moth's illness is fictional, the walk that supposedly spawned our bestseller is fictional, large parts of our past are fictional, and I can't be too honest about our current circumstances because that would involve saying 'We're successful grifters, newly rich and famous off the back of our own lies!
'So I will construct another largely fictional narrative about the Terrible Problems of Not Being Homeless Any More, how I wrote my bestseller as a way to jog my amnesiac, dying husband's memory, my mother's deathbed, which I am borrowing from a deleted bit of TSP, my Shy Woodland Creature childhood, how terribly hard I find it doing book events, not because I'm lying through my teeth, but because I am a Shy Woodland Creature, some purple prose about nature, and a holiday. Stick them together and that's a book -- right?'