what does it mean when someone says you have a tendency to be tangential?

Answer 1

Of, relating to, or moving along or in the direction of a tangent.
Merely touching or slightly connected.
Only superficially relevant; divergent: a tangential remark

Synonyms:
borderline, exterior, external, incidental, inessential, irrelevant, minor, outer, outermost, perimetric, secondary, superficial, surface, unimportant

Answer 2

Means you don't stay on one topic for very long.