What I understood by solo mining is mining with a single maching. I've been looking at the guide to make sense out of it.
The number of machines used is irrelevant, it could be 1 miner or thousands of them. Solo mining is mining a block without having to share the reward with other miners vs pools where the block rewards are split amongst all of the the miners in the pool.
To solo mine you just point your machine(s) at your own node (bad idea) or point them at a provider like the
Kano or -ck solo mining sites.