Neither. The test has items leveled by difficulty (not by grade level) from approximately preschool up through some high school topics. Examinees start from an item expected to be easy for them, based on their grade, and test until they trigger the discontinue rule (based on number of items incorrect in a row). This generates a raw score, which is converted to age-based norm-referenced scores (the standard score). With regard to the grade equivalent, that same raw score can be compared to the median score obtained in the standardization sample at each grade level (not literally--the curve of median scores by grade level is smoothed statistically).
So the OP's child obtained the same raw score as the expected median raw score for an 11th grader on that task, which included items of varying difficulty, ranging from preschool to high school. A couple of other factors: The median 11th grader does not actually answer all items correctly at the 11th grade level, so median performance demonstrates mastery at a level notably lower than 11th grade. And it's the raw score that is the same, not the actual items. It's possible for two students to obtain identical raw scores (hence grade/age equivalents), but to do so by, say, getting every item right all the way up to the ceiling, at which a series of consecutive incorrect answers ends testing, or by scattered accuracy up to a very high level (perhaps without a hard ceiling at all), with numerous gaps in accuracy along the way (such as often occurs in students with executive function/attention weaknesses, those with gaps in formal instruction, or those with certain learning disabilities). The second student may actually have a higher level of academic potential, but many gaps or inconsistencies along the way, for whatever the reason.
In short, he answered the same number (number, not necessarily difficulty) of items correctly that an 11th grader would have on the same multi-grade-level test. An impressive feat, but not one that tells you what his instructional level is, or what his mastery of either 3rd grade or 11th grade content is.
