Learn English – Meaning of “can’t tell if he’s coming or going”

This is quite a common phrase where I'm from...

'Saw you coming' is used to somewhat comical effect and what you saw was a reduction to the asburd - this would never be used in that context but instead, say, among friends:

Friend A: Check out my new branded watch, it only cost me £100!

Friend B: They saw you coming, it's a fake! [laughing ensues]

In this sense, what 'Friend B' is trying to say is that the seller would have known the watch was only worth, say, £25, and to somebody else may well have sold it it for such a price; but 'Friend A' was naive, or for whatever other reason, the seller had made a prejudgment (and preparations) based on experience which saw him trick you into paying a higher price.

The bottom line is that you were played, cheated, gazumped etc.

I believe this is a variant of "hello the camp", which is used as your father describes: when you're about to enter someone's encampment, as a kind of warning/greeting in lieu of knocking on the nonexistent door. (There's an elided "to" in there: the full/grammatical form would be "hello to the camp".)

I imagine "hello the fire" could be used if there isn't an encampment to speak of, just a fire with guys sitting around it.