Trace amounts were detected in the melt water. Plutonium does not exist in nature, all significant amounts are man made. I think it's likely that that plutonium came from the lost RTG fuel rods. The article explicitly mentioned that the American climber was tasked with handling the fuel rods and loading and unloading the device. They lost it at their base camp, not where they intended to deploy it. I believe that would mean that most likely the fuel rods were not yet loaded and sealed into the device and were instead still inside whatever lead lined box they were transported in. I don't know what the actual fuel assembly would have been for a plutonium RTG fuel rod from the 60s but I have a feeling it wouldn't stand up to 60 years worth of corrosion in a wet and warm environment outside of the generator it was supposed to be assembled in.

As for the radiation amount, I meant in the hypothetical scenario of comparing it to a lost but undetonated nuclear weapon which would be substantially less radioactive. I'm well aware of what a half life of an isotope is. The half life of Pu-238 is basically as bad as it gets because at 87.7 years it'll take a substantial amount of time for the radioactivity to subside yet as far as half lifes go that's pretty low and would still be highly radioactive. Pu-238 in a water source is pretty bad and while it might be trace amounts now, if the fuel rods are compromised after all that time they're only going to get worse and start leaching out more and more.