At the most basic level "intellectual peer" would be in contrast to "age peer." It represents the complexity of language, ideas, interests over the coincidence of birthdays.

Some gifted kids will fit in fine and adapt with their age peers doing many things. Others are really caught up in their world of ideas and the way they think about them, they may not be able to dial it back and will tend to gravitate to adults and much older kids.

A six year old who says things like: "I am fascinated by the implications of mixing liquids of various PH levels; so, let us sneak into the back of the cafeteria and borrow some." might not get the most receptive of audiences on the playground to their ideas or conversation. So here, the asynchronous nature of gifted has a mix of a certain interest above age level and the common sense of a six year old. This kid might find an eight or nine year old who is interested in their idea, but could also be mocked for the bad plan.

Not sure if that clarifies it enough, but that's the basic concept in my mind.