Interesting.
That is definitely not the same as the end that came out of the slave cylinder, but it is the same as all the hoses I've been given trying to order new ones.
Now I'd better go look down in there and see what the slave cylinder end looks like. I'd assumed that the hose that came out was the right one.
I bet the previous owner just grabbed a random brake line that threaded in and cranked it down REALLY HARD until the copper washer acted as the seal. Which is probably why the hydraulic clutch always leaked and needed refilling.

Thanks!