The statute is quite explicit that "Misuse of a transfer, pass, ticket, or token with the intent to evade the payment of a fare" is an offense -- using a cheaper ticket to avoid payment of the full fare falls within that language.
While buying the wrong ticket may help support somebody's claim of mistake ("I thought I bought the correct ticket at the correct price"), the fact that you bought a cheaper ticket is not evidence that you did not do so with the intent of committing fraud by using that ticket to avoid a higher fare.

