that's so, but the legend is "lee and perrins were told to recreate a thing that the governor of bengal's wife had liked when they were in india, thought they failed, let it ferment, then claimed victory", which isn't quite Thailand.
Is it actually fermented fish? I happened to be looking at its ingredients earlier this evening before I saw this post (really! wild evening) and it merely lists 'anchovies'. The top two ingredients are vinegars, which suggests to me the flavour's approximated by pickling (cf. cucumbers, kimchi/sauerkraut/coleslaws, etc.) rather than merely a preservative.
It's not very similar. The fish in Worcestershire sauce is mild enough that you might not notice it if you didn't know it was there. It's vinegar + molasses + tamarind + salt + sugar + spices, with the fish just there for added umami taste. Thai fish sauce is only fish + salt + sugar, and it's unmistakably made from fish.
Agree the fish sauce itself is clearly different, but I'm less confident about the flavor profile as a whole. Maybe that's just because of the tamarind though.
Edit: Worcestershire sauce's flavor comes from fermented fish + tamarind, which also are two major ingredients in Thai/Vietnamese cooking.