In this case, the OP is in Northern Ireland.
They had a phase of deploying FTTC that finished a long time ago, but NI has different geo-demo-graphics ... they have considerably longer D-sides than England, so less homes qualify as "superfast". Where England can translate 93% fibre into 89% superfast, NI translates 95% fibre into only 76% superfast.
This second phase in NI is more about converting those with FTTC, but still a long line, into proper superfast properties. A lot are being done with all-in-one cabs (combined PCP and DSLAM), added into long circuits. Some get FTTP - presumably for cost, density, or distance reasons.
We'll see more of this in SEP phases in England, but for now the 90% targets can be hit with just standard PCP upgrades, combined with adding DSLAMs for EO lines.
However, one county is getting FTTP infill in the way you think - Surrey. But that is because their first phase was over-funded to reach 99.7%, and they are chasing stragglers now.
As for the pole-mounted box...
Right now, it looks to be infrastructure for FTTP only.
Some architectural diagrams have surfaced that show a similar box in use for FTTRN - so that was plausible, but less likely. I don't think an FTTRN box has been sighted in the wild yet, apart from trials, let alone the pole-mounted adjunct - FTTRN is, at best, still on trial, and at worst, pushing up the daisies. Things have gone very quiet.
Having seen the box pictured for both FTTP and FTTRN architectures, it isn't a huge leap to believe that they could be used for G.Fast deployments too - which will need similar jointing as FTTRN, deep in the network. Again, not confirmed in the wild, and only in small trial areas anyway. A long way off...
Note also that these boxes are only going to be seen with aerial distribution of fibre - ie the fibre itself runs pole-pole-pole. If the distribution runs underground, and only the final drop to homes is from the pole, then the boxes will be in the underground chambers, and look entirely different.
No way to tell how full the cab is, apart from a costing an Openreach engineer when he's at the PCP. Then he can tell from the number of tie pairs being used.