A spam post could be deemed so due to the context of the thread:
Suppose there are already 10 replies, of which highlight similar solutions or remarks about the given topic. If you decide to write an 11th reply and fail to add anything of substance that is novel, then you are merely repeating the previous replies in the thread and thereby not contributing to the discussion. Thus, insubstantial quality - multiple posts of this kind in quick succession would likely be considered "burst posting".
Pedantry does get tiresome, doesn't it?
It looks logical. But I would like to see a comment from administration: Is it forbidden to post to thread if the post is not offtopic but out of context (as it described above)?
Look at example:
start post: bitcoin will grow because will halving.
post 2: halving does not affect growth because: fact1,
fact2post 3: halving affects growth because: fact3, fact4
post 4: I think this we can not get a consensus because: fact5, fact6
post 5: I agree that bitcoin will grow because will halving:
fact2So "post 6" is a spam and author should be banned?