Welcome!
The base note in LMMS is A4 or La4.
The base note is represented by the green square above the piano keys of the synths.
This base note can be modified. If you open the Bit Ivader (for example), and you press the Y key on your keyboard, what you hear is the note A4. If you move the green square to the left and press the Y key, you get a higher note than the la4. Etc.
Since A4 is the base note in LMMS, when you click on a browser preset, the note you will hear is a A4 (well, I have not checked if it's true for all presets).
Does that answer your question?