Interesting question; I learned something in answering it! I'd never heard the word scattershot specifically; I guessed from context that it was similar to (if not exactly like) a "fair-weather friend"; someone who's there only part of the time, depending upon how easy/difficult it is to be a supportive friend at the time. Google defines scattershot:
denoting something that is broad but random and haphazard in its range.
Dictionary.com provided some interesting insight. First, the definition:
scattershot, adjective
- random; haphazard: their approach to conservation is scattershot and unscientific
And now for the interesting part, found further down the page in the Word Origin and History section...
adj. 1959, figurative use of term for a kind of gun charge meant to broadcast the pellets when fired (1940), from scatter (v.) + shot (n.).
For me, at least, this made the word make much more sense. The word scattershot would therefore be akin to "hit-and-miss", which also has origins in weaponry; you take a shot, and sometimes you get a hit and sometimes you don't, and you're never really sure if or when/where a pellet is going to make contact.
Figuratively, in our scattershot friend example, we replace "pellet" with "efforts at acting like a friend"; the speaker never knew if or when he could count on his friend, so rather than terming him "a reliable friend" or "an absentee friend", he struck the middle ground: "a scattershot friend", who may or may not be there when I need him.
