or....it could just be poor technique
I seriously doubt that and apologies for having doubted you in the first place. You're clearly far more accomplished than I.
You were right; clicking through to the image on Flickr does show it as pin sharp.
I had a look through your sets and there were almost too many tag as favourites for it not to be embarrassing! I was particularly keen on the lighting you capture in many of the portraits and some of the landscapes. The one of Ullswater springs to mind in particular. Reminded me a little of Don McCullen.