> As far as my current understanding goes
Your understanding is wrong.
JTables work with two different objects for Cellrepresentation:
TableCellRender and TableCellEditor.
As you already recognized the Editor is used to change the Cells value.
The Renderer-Object is used to Display the Cell while it is not in "editing" state. Unfortunately the Cell is in "not editing" state when you click on it (the first time) or move the focus to it. That's why the Renderer object is getting this click/key event rather than the Editor Object.