If I understand correctly, first, it should be highway=pedestrian rather than highway=footway because it is wide enough for motor cars, as stated in Thailand Wiki. ( https://wiki.openstreetmap.org/wiki/WikiProject_Thailand#Rough_guidelines_for_minor_highway_tag_decision-making_(useful_in_most_cases) )
Second, highway=footway + area=yes is for non-linear footway, according to the wiki. The area that you have tagged is a linear one, so it should be area:highway=*.
Furthermore, I think tagging it to be rendered violates the "Don't map for the renderer" principle of OSM.
Regards