Lightroom is not simply taking your pixel, converting it to HSL, increasing S, and converting it back unchanged in every other respect. Its adjustments are done in a wide-gamut internal workflow (commonly described as ProPhoto RGB–based), and profile conversions or export color-space changes can also shift measured values.

Based on the shared tests, a pure Lightroom Saturation increase caused only a very small hue change when kept in the same color space. Larger shifts appeared when color profiles changed, such as working in a wider space and then exporting to sRGB.

So the most likely explanation is:

• Lightroom’s saturation control is not a simple HSL/HSV S-only edit.
• The image may be processed in a different working space than the one used to inspect values.
• Converting between profiles/spaces can change RGB numbers and slightly alter derived HSL/HSV hue/lightness readings.

In short: yes, Lightroom uses its own internal processing pipeline, and the hue/lightness changes you measured are likely due mostly to that processing plus color-profile conversion, not a straightforward HSL saturation operation.