I think you're right, TiVo would record the repeat if it had missed the program completely, but as you say, don't think it would re-record if it got a partial recording.
Although on thinking about it, rather than being a feature, is this not just the issue that "New only" doesn't exist for V360 series links, so the repeat would have been recorded even if you hadn't had the issue that stopped the original recording? So it's a bug that's worked in a helpful way on this occasion, and may actually disappear as a feature once the bug is fixed.