It seems he's between a stall and a hard place here: his thank you note for the prosecutor's cooperation isn't merely perfunctory in context with the dropping of other charges that would have placed more salacious (and damning) details of this event in the public record. (I have no idea whether those charges would be back in play now.)

His stance that he was rushed into making a plea from naivete and confusion appears to be contradicted both by his long experience as a lawmaker who was strategizing about public relations at the outset -- not calling a lawyer seems more related to PR than ignorance about his rights -- and the fact that he and the prosecutor had several exchanges, over an extended period, to expedite this matter quietly (also with PR being at the forefront.)

So thanking the prosecutor for his cooperation seems to relate more to Craig making his personal interests and requests known at the outset than being passively kept ignorant of his rights and denied them.