Why was "are we getting together with Keoki?" marked wrong
The difference is between "are we getting together with Keoki" and "are we going to get together with Keoki?". Its a matter of tense
It's marked correct now, since we commonly use that in English to refer to the future!
What Lois985131 said. I don't see a clear difference, although since both versions are natural English there must be some reason we'd choose one of them.
What indication is there for choosing "get together" over "socialize?"
I'm curious. What's the difference between "going to get together" and "getting together"?
"Going to get together" is future tense.
"Getting together" is present tense. (Though we often use it to indicate near future in English.) I think the course makers want to emphasize that e ... ana is the future tense.