that block reward went to a address 3KZDwmJHB6QJ13QPXHaW7SS3yTESFPZoxb
that address has received over 1600btc in 7 months
thus it is a pool or a asic farm with alot of hashpower. it just did not announce its name/brand/company to the explorers tags
based on some basic math of ~200 days and 1600btc. thats more then 1 block a day. meaning about 1% of the hashrate of the network was used to get those block rewards
..
technically there are pools(well lets just call them self managed asic farms) where they do not host for outsiders. where they only operate for their own devices.
..but now we are getting into the semantics of where is the line of whats defined as "solo"
...
as for those shouting about the CK pool.. no its not a real solo mining, because its still uses a pool with a pool manager.. and so its not a solo effort where people make their own individual blocktemplates and transaction selections.. its instead simply that the CKpool manager does the transaction selection and hosts communications with the workers and its ck pool that assigns that each of its workers gets a header with a coin reward that rewards the pool worker the majority of funds.. but the ckpool manages the rest.. so not really "solo"
in short there is still a pool involved.. its just the reward share which handled differently
the last time someone(home hobbiest) actually solo mined (ran their own software to make a blocktemplate, collate transactions, set their own reward address and broadcast the result to the network from his own node.. .. with no pool/server/manager remotely).. was a long long time ago