No, it suggests Marisa is wondering if it's alchemy. Not the same thing.
No, it CONFIRMS Marisa is wondering if it's alchemy. Not the same thing.
In addition to this, assuming Marisa can be taken at her word (because she states the way the spell card works as a matter of fact), it also confirms that Patchouli is capable of synthesizing jewels by hurling mudballs.
Webster.com defines alchemy as :
1: a medieval chemical science and speculative philosophy aiming to achieve the transmutation of the base metals into gold,
2:a power or process of transforming something common into something special
3: an inexplicable or mysterious transmuting
If, in fact, the spell card is indeed "synthesizing jewels by hurling mudballs", which is what Marisa claims it does (and I personally think it's difficult to imagine her screwing up that observation, given that Patchouli throwing mud balls that transform into gems right in front of your eyes would be a pretty difficult thing to miss), then it does indeed match the definition of alchemy.