All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah and that Muhammad is His slave and Messenger.
According to what is mentioned in the question, it seems that what happened is a marriage contract because its pillars and conditions - the eejaab (offer) and qabool (acceptance), the presence and consent of the guardian (wali), and the presence of witnesses - were met; so the girl then became the wife of that man.
The claim of that man that there was a misunderstanding, then in principle there was no misunderstanding, so the view that should be acted upon is what is evident from the circumstances until proven otherwise.
There is a rule stipulated by some scholars that if a person’s statement contradicts what is apparent, then this is only a claim; in which case he has to provide evidence; and the one whose statement is in conformity with what is apparent, then it is sufficient for him to make an oath. An example of this would be what Al-Mahalli said in his commentary on Al-Minhaaj: “If the husband and wife embrace Islam before they consummate the marriage and the husband says, ‘We have become Muslim together, so the marriage continues [is valid]'…then it appears that he is a claimant; because what he had said is contrary to what is apparent, and she is a defendant (i.e. it is sufficient for her to make an oath because her denial is in conformity with what is apparent)...”
As regards spending on the wife and the like, then this does not become obligatory as soon as the marriage contract is conducted, but this becomes an obligation when the husband is enabled to have sexual intercourse with her and she lets him do so; Ibn Qudaamah said, “In brief, if the wife offers herself to her husband (for him to have sexual intercourse with her) in the way that she should, then in this case she has the right upon him to provide her with her needs, such as food, drink, clothing, and accommodation…”
Allaah knows best.