Here follows the answer - I am embarrassed that I know such boring information -
The GT TDi was originally launched with the 110Bhp and same spec as non turbo GTi - this was slowly upgraded - 115 - 130 and then from about 2002, a GT TDi 150 was available (came with spec as per GTi 1.8T).
The only non 'GT' TDI engine in the hatch range was the 90bhp - available as S or SE - think this may have been upgraded to 100bhp at the end - but non - sporty spec. The more powerful TDI's (130) were available in the Estates in S or SE spec I think.
So, to cut a long story short.....
Your mate is either looking at
1) both are GT TDi's just not advertised correctly
2) ONe is an estate
3) MOST LIKELY - one is a parallel EU import and branded TDI not GT TDI - but has the same spec as the GT TDi. IN Europe the 2.0 GTi is just branded 2.0 - hence you see lots of Golfs with 2.0 on its rump, whereas a UK car would say GTi. Loads of GTi's and TDI from the large car supermarkets are like this
As far as red t's, d's and I's are concerned. Orginally the 90bhp was all silver, the 110 had a red eye, then when the 130 replaced it it had a red D and I - and some 150's are all red. However, its all screwed up, as for the large part, the dealer fits the badges, so I know colleagues who asked for differing badges etc.
I would like to point out that I am not a complete saddo geek - I purchased 5 Golf diesels for my company some years ago, so I swotted up on this. Ended up getting boggo 90bhp 's' models