Quinnipiac as a rule does not push leaners hard. That 6% is very surprising and can be very bad news for Senator Menendez. Either the undecideds are breaking really early for New Jersey or the Big Q pushed them and they are not leaning towards breaking for him.
If the election were held today, Kean would likely win. The bad news for him is that the election is still 6 weeks away and people can change their mind.
Without leaners its 41-38% in favor of menendez so it looks like they may have pushed the leaners pretty hard to have that much of a disparity.