Why is 'date' in the plural in this sentence

[dut_thinker]

Dear teachers

Why is 'data' in the following sentence in the plural?

I muddled (up) the dates and arrived three days late.

Thanks in advance.

[J&K Tutoring]

Perhaps the event was held on the 16th, but you thought it was to be on the 19th. Two dates were involved in the 'muddle'.

[dut_thinker]

Perhaps the event was held on the 16th, but you thought it was to be on the 19th. Two dates were involved in the 'muddle'.

Thank you for your answer. I got it now