The whisky was not matured in the exact same sherry cask. Look at the bottle of sherry: it says L1/14. If the sherry was taken out in 2014, it is impossible that they filled it with whisky in 2012.
The whisky was matured in one of the barrels from the Oloroso solera at Tradicion. Tomatin makes it sound like a single barrel sherry, but that the concept of a single barrel bottling is very, very rare in the sherry world.