The typical 4 traits remind me a lot of INF's moreso than ISFJ's. I think it's a lot more natural for an INF to be constantly examining themselves, where they stand in the big picture, who they really are, and how they're unique. They also tend to be more likely to idealize things.
ISFJ's seem to be a lot more concerned about pleasing others, making things run smoothly, and keeping consistency. We just seem simpler, I guess. It seems to lend itself to us being more likely to conform rather than want to be unique.
I think more than anything it goes down to the S/N difference. N's are more likely to look to the future and "what could be", whereas S's just focus on the issues in front of them more. SJ's in particular like to value the past, traditions and consistency.
So it's possible that you're just a lot closer along the S/N line than most ISFJ's.
I've read that it's very common for ISFJ's to be 1's, though, along with 2's, 6's and 9's. As far as the 5...like I said, I once tested that way. I've read ISTJ's are often 5's, and they're very similar to ISFJ's. I also picture 5's as being very INT like as well.