Fernando, I really see no problem with terminology at all.
Tim has given us the meanings of the terms, as they are used in the trade.
Gonzalo has reinforced Tim's explanation with a further trade reference.
I have given the meanings as they would be understood by an educated native English speaker who is not a silversmith or jeweller.
The link I provided in an earlier post sets out a very clear explanation:-
http://en.wikipedia.org/wiki/Repouss%C3%A9_and_chasing
In common usage, I believe most native English speakers would refer to the work as "embossed". Although not strictly correct, this is completely acceptable, and incidentally comes close to your "stamped" meaning. Modern English grammar is concerned more with the way in which words are generally used, than with strict dictionary meanings.
However, what is of interest here is the opinion of your jeweller consultant that this work was done from the inside of the scabbard.
To my knowledge, the skill to create this motif from the inside of the scabbard has never existed in Jawa, nor in Indonesia. I am very familiar with this type of work, and it is done from the outside, after the scabbard has been fabricated. Tim, who is a skilled craftsman in this work, seems to be also of the opinion that it has been done from the outside.