As has been previously pointed out, there was no notification requirement. Even if there had been, the recourse would have been a suit against the seller for failure to disclose. That would have no impact on the development.
Something else is that this appears to be a senior development. Senior developments don't generally have the same impact on a neighborhood as "regular" low-income housing. The 45 units will probably have 60 - 90 seniors living there (assuming 50% couples). The information about the other development that was denied said that "standard" developments have a density of 10 units per acre, and that one was denied had a density of 30 units per acre. This is a 2.3 acre lot, so "standard" would be 23 units, while "overdeveloped" would be 69 units. 45 is right in the middle.
If their senior development is denied, they'll probably come back with fewer units, but no age restrictions. 23 units with a single mom and three kids each may not be as peaceful as 90 seniors.