When generating vector formats like SVG, MATLAB uses a heuristic to determine how to export the content. In your case it appears that adding the contour has caused the heuristic to choose to embed the content as an image, rather than as "true" vector content. You can override the heuristic by doing one of the following:
% Assuming fig is the handle to the figure you are trying to save...
% set the figure's Renderer property to 'painters' before saving as EPS/SVG:
set(fig, 'Renderer', 'painters');
% If saving as an EPS file, in R2020a and later, you can use the exportgraphics command and specify the 'ContentType' as 'vector':
exportgraphics(fig, 'output.eps', 'ContentType', 'vector');
% For both EPS and SVG, you can use the print command and include the '-painters' option:
print(fig, 'output.svg', '-painters');
I hope that helps.
