If it had been bred & reared in captivity & then later released/escaped, then I doubt very much it would have reason to fear humans...
The Tayside Beaver Study Group (which is very different to the Tayside Beaver Spotters Club
) state on their website that the Tayside beavers have nothing to do with the trial in Argyll, which I believe were reared in captivity.
They also say that SNH and "other Agencies" first became aware of Beavers in Tayside in 2006. I believe anglers were aware a couple of years before this.
So, I think the Beaver I saw would possibly be a descendent of those first tayside beavers and born in the wild?
Looking up the Eurasion beaver shows a lifespan of 5-10 years in the wild so possible.
I would like to think that no illegal introductions have happened recently, mainly because the keeping of beavers as "pets" has been strictly controlled as a license is required.
Who knows...but I will take my camera next time.