Well I believe that you are both right. Both situations are possible.
If the caliper piston is hard to turn/move even with the bleed nipple slackened off, then the piston is corroded. It can be cleaned up (using a wirebrush mounted on a bench grinder) - don't try to clean the aluminium bore in the caliper - and as Jo said, don't try to remove the rubber seal, just press the brake pedal until the piston comes out. You can get replacement seal kits and I have replaced them in the past, but to be honest, it's rare to see a leaking caliper.
Seized/sticking pistons were a common problem with X1/9 front calipers, which are practically identical to the Uno calipers.
Meanwhile a blocked brake hose causes the caliper to stick 'on' because the fluid, while pumped in past the restriction under pressure, cannot escape because there is no pressure generated by the caliper to push the fluid back.
I imagine in a dry place like South Africa it is less common to see piston corrosion problems, which are due to water absorbed in the hydraulic fluid (from atmospheric humidity, etc.) and possibly salt water from the outside if the seal is damaged and the brakes are really drenched in winter driving.
There is also the third possibility that the wedges on which the caliper slides could be rusted/seized.
-Alex