Rambam in Sefer Hamitzvos #11 and in Mishne Torah Hil. Talmud Torah rules that studying and teaching Torah are one Mitzvah:
היא שצונו ללמוד תורה וללמדה וזהו הנקרא תלמוד תורה,
והוא אמרו ושננתם לבניך
We can see that in many other cases he seemingly splits one commandment into several distinctive Mitzvos, like two Teffilin or honoring and fearing parents.
In many cases, the Gemmorah wants to emphasize G-d's intention to multiply our merits by doubling our Mitzvos (or transgressions) so it would be plausible to count it as two Mitzvos.
Also there are numerous different Psukim for either learning or teaching Torah, for example, the Posuk:
"וְשִׁנַּנְתָּם לְבָנֶיךָ וְדִבַּרְתָּ בָּם בְּשִׁבְתְּךָ בְּבֵיתֶךָ וּבְלֶכְתְּךָ בַדֶּרֶךְ וּבְשָׁכְבְּךָ וּבְקוּמֶךָ"
can be understood as two: ושננתם (teach) and ודברת (learn).
So why did Rambam combine the two into one Mitzvah?