The notion of friend in the Conflict of Interest Act is something that refers to public office holders, including ministers and appointees. To my knowledge, the definition is not in the act but this is done as part of the commissioner's analysis on the facts.
In your question, you asked whether the same requirement should apply in the context of MPs' work, whether the requirement level that applies to ministers is necessary for MPs, given the context in which MPs carry out their role. Or is the more general notion of “unduly” sufficient for these purposes?
Certainly, when comparing the two, it can be seen that in the act the bar is set higher for ministers, as the definition explicitly includes friends.