It is not true that this result was previously known. Please see the section “Comparison with related work on Monero linkability.” in the paper (https://monerolink.com), which starts "We note that earlier reports from Monero Research Labs(MRL-0001 [10] and MRL-0004 [7]) have previously discussed concerns about such deduction, called a “chain-reaction,” based on similar insights as described above. However, our results paint a strikingly different picture than these." and then goes on to show those striking differences in the new results and the previous knowledge.