OK, so I was apparently not looking at the correct line as this line does reference a channel definition:
{"type":"channel","channel":{"team":"company","name":"c047u3dh05p","display_name":"c047u3dh05p","type":"G","header":"","purpose":"Group messaging with: @first1.last1 @first2.last2 @first3.last3 @first4.last4 @first5.last5 @first6.last6 @first7.last7 @first8.last8 @first9.last9"}}
Not sure where channel definitions are documented at this detail level, but could this be unsupported? It would be useful to know all supported channel types, maybe I can just assign it a supported channel type.