The meter of this line is dactylic.
A dactyl consists of one stressed syllable which is followed by two unstressed syllables. So here, I will write the stressed syllables as "-" and unstressed as "U".
Galloping madly he quickly arrived = -UU-UU-UU-
Ga- is stressed, lop and ing are not. Mad is stressed, ly and he are not. Quick is stressed, ly and a are not. Rived is stressed.
Anapest has one unstressed syllable followed by two stressed ones. Trochee and iamb refer to two syllables, not three.