MySQL Cluster - Got error 1601 'Out extents, tablespace full' from NDB
First 2500*50kB ~= 128MB. Then if you will check CREATE TABLESPACE syntax default INITIAL_SIZE for the datafile is 128MB!

So if you want to store more data you can either specify INITIAL_SIZE you need while creating tablespace or you can ALTER TABLESPACE ADD DATAFILE.

By specifying STORAGE DISK in CREATE TABLE statement you stated that you want on disk table not in memory. With such tables ALL REPORT MEMORYUSAGE shows nothing meaningful for that table.

If you want "classic" NDB table which is stored in memory just skip TABLESPACE ts1 STORAGE DISK modifiers and then ALL REPORT MEMORYUSAGE will show you how much memory is used for the data and indexes.