Another possibility is the stratum/pool mining software responsible for this block is not connected to a full node, rather a lite or SPV node.
That block mined by BTC.com pool[1] which even have their own block explorer[2], so this possibly is ruled out.
Running a bitcoin node again, is quite resource intensive - and the disk space alone is 405Gb (standard, not txindex) - I can fully see a situation where some clever software simply listening to the headers could work.
Quite intense for average user, but not for pool who have 4.94% share in last month[3].
Usually this happens when two blocks are mined within a few seconds of each other.
I also agree with this possibility. In last month, BTC.com only mined 2 empty blocks among 222 mined blocks[3].
[1]
https://pool.btc.com/en[2]
https://btc.com/btc[3]
https://btc.com/btc/insights-pools