This block signaled support for BitPay's adaptive Block Size Proposal and was mined by slush pool.
I asked slush this exact question on twitter back in 2016!
Note that this answer is not entirely complete, because the BitPay proposal specifies:
Miners express their support for this BIP by setting the
fifth-highest-bit in the block's 32-bit version number (
But these blocks as you note also set bit 2 (
0x00000004) which was not addressed by slush in his answer.
During this era, several other soft-fork proposals were being floated around that (due to lack of coordination a.k.a. decentralization) collided on their BIP9 signals. One was Extension Blocks. I'm having trouble finding links but I believe also at that time there was Rootstock (RSK) proposal that defined bit 2 as the signal, and an anti-asicboost proposal by Greg Maxwell that also signalled bit 2.