I took a quick look at your account…
There are ~200 invoices on the account (Sales and Purchase), each single line invoice would post 3 nominal ledger entries (non VAT invoices are typically 2 entries), which would bring you to around 600 entries. You then have around 300 bank entries, each bank entry would consist of 2 nominal postings. This would take you over 1,000.
We try to explain a bit more about how we determine account size here. You can also check the exact postings and backing calculations in Account Settings >> Company Settings.