The active chain is always the longest chain. Somebody was smart and saw the only thing preventing upgraded node from connecting to old nodes was to check the version number (which can be changed easily).
The "old chain" was the longest/chain with the most work so it became the active chains. Upgraded nodes are now on that chain or stuck depending on circumstances.
On top of that, I haven't been following PoDC much I guess PoBH seems to still be accepted by "upgraded" nodes so they're accepting these blocks.