Building From 1700 To 1843
The picture supposedly shows the house in 1845 so either the picture source is wrong or the plaque is.
In the early 18th century Abney Park was laid-out by the recently widowed Lady Mary Abney, assisted by Dr Isaac Watts and the neighbouring Hartopp family. In about 1838 the house became a Wesleyan seminary but in 1843 it was demolished and the materials used for constructions elsewhere. The Park was opened as a cemetery in 1840, so it's possible the house demolition took place while burials were going on.