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State which line is fitted
The public tool fits Y=a+bX. A through-origin model forces a=0 and estimates slope from uncentered sums. That restriction should come from the modeling task, not from an attempt to remove an inconvenient fitted intercept.
Inspect the original mean context
In the original record, x̄=0 and a=1.2%. A through-origin line cannot pass through the centroid (0,1.2%). Its residual sum is not forced to zero by an intercept normal equation.
Keep the statistic definition attached
The standard intercept-fit R² and its equality to squared correlation should not be exported unqualified to a no-intercept calculation. A different fitting criterion or score definition answers a different question.
Retain a supported restriction
If zero intercept is required, document that model and its appropriate formulas separately. The tool does not silently switch between those models or suppress the intercept.