From a followup tweet, it seems they just want to stop misleading listings. I don't think the Geany listing is misleading.

Rafael Rivera @WithinRafael

> Update: 10.8.7 will be edited (no timeline) to reflect Microsoft's intentions to block misleading non-free open source listings (e.g. 7-Zip clones) and not flat out block the sale of open source software in the Microsoft Store.