How long have you been at this? Because if you can't recognize functions or at least attitudes (such as this person seems much more Pe than Pi) then you're going to be highly confused by behaviors. A person can BEHAVE this way or that, and indeed it may be some indication of type, but what is more important is the motivations and thought processes behind the behaviors.
Mixing up ENFPs and INFJs is pretty extreme, because ENFPs are actually more similar to other FPs, and maybe even occasionally seem like immature or crazed ExTJs under stress.
It's a very subtle thing to have to learn, it's taken me years to understand and grasp the functions and spot them, and it tends to go best for me with people I'm very close to, and I understand how their mind works.
Differences for me have sometimes come with the secondary function rather than the primary. Like my ESFJ sister, I thought she was ENFJ.
Or I'll be good at judging functions like my own are absolutely Fi/Te...but I had to clarify differences between Se and Ne, and I realized that I enjoyed my supposed "Si" way too much to be an ENFP, but seemed to be using some forceful "Te" that made me seem un-INFP-like...looks to me like I was confusing my Se for a weird mix of Si and Te.
What's funny though is that even on the Keirsey site they have me pegged as an SFP. So there's more overlap I think than people may give credit for, if they really understand what they're doing.
Like how my ISTJ mistook himself first for ISFJ because of high Fi, and I thought he seemed ISFP-ish at first because of that Fi. People also called him ENTP and ISTP because of his BEHAVIORS and PERSONA.
However, getting to know him, he's a painfully obvious Si dom, and over time it became obvious that he's Te/Fi. He even relates to the Keirsey idea of the SJ Guardian.
So does my ESFJ sister, incidentally.