There is no reference to what is in the planter boxes — they could be empty, for all we know — so you shouldn’t assume that’s the issue, which in any case it clearly isn’t.
The planter boxes have been placed there as a physical barrier, according to Roland. This isn’t a gardening question, it’s a matter of what strata committees can and can’t do on common property.
But, yes, drainage from planter boxes used for plants is a concern, and thanks for pointing it out.