Well,Nicebutdims leaf looks completely different to mine,but as I've stated before mine came from a plant that acheived epic proportions last year.So difinitely a thai giant.
Your plant Amber looks very much like mine did when I got it last summer,with an almost heart shaped leaf.Same colour to the leaf aswell.
Found a couple of pics from early spring that shows the difference between the 2

- Normal gigantea

- Thai giant
I'd be well satisfied with what you've bought,as the seller looks like he knows his stuff.
His musas look very appealing,especially as I lost a huge amount of my own collection.
I'm sure he wouldn't risk his reputation selling duff plants as I'm sure he must be well known on some of the german forums growing what he's got