When using parametric function for plotting a circle like:

r = 2;
xc = 4;
yc = 3;
theta = linspace(0,2*pi);
x = r*cos(theta) + xc;
y = r*sin(theta) + yc;
plot(x,y)
fig2plotly();

We get circle plotted in polar system of coordinates

Suppose this can be because in this case plotly figure data.type is 'scatterpolar' instead of 'scatter' for other usage of plot(x,y)
Example of circle using parametric and plot(x,y) is in:
https://www.mathworks.com/help/matlab/ref/plot.html#buqplgq-1