hi and welcome to the GMB.
could be wrong, but I sense from your comments that you half expected Christies to confirm a Spanish origin for this glass. Pre-owned objet d'art, whether modern or genuine antique, travel a great deal in their lives - sometimes surprisingly so, and although this may well be French in manufacture, suspect it's typical of pieces that might have originated in more than one European country. Presumably the auction house didn't explain their reasons for saying French, but obviously there was something in the appearance that induced this comment - it might have been the acid/matt finish on the stem, or the spiral of green decoration. Wine/hock goblets/glasses are common to most countries.
Regret we don't always have the answer, and you may not get any further with this one - however, it's an attractive glass