‘Hana Festa Memorial Park’ is a translation error due to the lack of language skills of translators.
The correct notation is ‘Flower Festival Commemorative Park’.

In Japanese, it is written as '花フェスタ記念公園'.
The meaning of '花' is a flower.
'フェスタ' is an abbreviation for the festival.
The meaning of '公園’ is a park.
In Japanese, '記念' has two meanings: 'commemorative' and 'memorial'.
Because it ’s a botanical garden, not a graveyard, “Memorial Park” is wrong.

Please refer to the following URL.
http://www.hanafes.jp/hanafes/aboutus/english