No, he isn't. He is one of many developers who have worked on the PartDesign workbench over the years. The first developer who actually created PartDesign was FreeCAD's founder jriegel. There were a few others who helped around 2011-2012, among them mrlukeparry and logari81 (who also created the first implementation of the Sketcher solver). In 2013 jrheinlaender was the one who did the initial ground work on what would be known for a 2-year period (2016-2018) as "PartDesignNext". His code sat abandoned in a separate branch until a small team made of ickby, DeepSOIC and others I forget (sorry) salvaged it by the end of 2015. ickby was the de-facto lead (and sometimes only) dev for about 2 years then he stopped working on it around September of last year. Since then, PartDesign has been orphaned again; even though some devs occasionally commit bug fixes and enhancements, none of them has officially taken charge of its long term development.
Most of what has been discussed here predates ickby's involvement. I'm pretty sure PartDesign Groove was developed by jrheinlaender. He's the one who created the wiki page back in 2012.