OP (me) copy-pasted the title exactly from the source page. Assuming the title at time of copy-paste was "3,000", I don't know how it became 3k. Is there an automatic search replace done by the HN submission process?
There is - on one occasion a submission of mine had the capitalization automatically changed (incorrectly as it happens). I don't know if this is what happened to you, but it seems likely.