Jaller
TL;DR: It's most likely an alternative name. I will edit the map accordingly.

The community centre answered:
"For events and programming we generally refer to it as trimble park as it is a more specific name, and helps people find it. Im not sure about the history though or if it was possibly changed at some point in time."

City website using it as an alternative name:
https://vancouver.ca/parks-recreation-culture/wading-pools-and-water-parks.aspx