I pointed this out earlier, and then retracted my conclusion because I spotted an error in the reasoning.
It was a narrow-topic thread. I think post IDs are assigned not sequentially within a thread or bread, but sequentially within a board. A slow bread (as is common on a narrow-topic thread) will not get anywhere close sequential post IDs, because most IDs are eaten up in other (faster) threads. So the post IDs assigned in the slow thread will be widely spread out, accounting for the wide range of post IDs (over several thousands apart) that made me initially skeptical. The actual bread, as archived here, has 687 posts (which fits easily in a bread.) The wide spacing of post IDs makes sense as legitimate in the context described above. Any claim that it's fakery because of the widely separated post IDs must overcome this rebuttal.