We had an expression when we were kids..."accidentally on purpose". No, this wasn't some serendipitous discovery, but a targeted information gathering operation aimed specifically at Trump's people. Interesting how the debate has shifted, though, because if anything had been found that was actionable, that would be all over the front pages.
Again, I think we need to draw the distinction between the incidental collection, and what happened next. If Nunes is to be believed, the collection itself is legal. Which among other things means that Trump's people really were in contact with people who were under surveillance. Though it's highly unlikely that they were not the only ones.
It's what may have happened next that's the real problem: the intel people failed to "mask" at least some of those they should have. That's bad enough. But if they
selectively failed to mask, then that's a much bigger deal.