What does Amazon SES free tier mean? Why am I charged?

I recently got some bill from Amazon SES service. I thought I was in the free tier limit which means I can send 62,000 messages per month to any recipient:

https://aws.amazon.com/ses/pricing/

I am ok with the fee, however I don’t quite understand why. Is it because I am not using EC2 instance?

You can send 62,000 messages per month to any recipient when you call
Amazon SES from an Amazon EC2 instance directly

If I am not using EC2 instance, they charge $0.1 per 1000 emails I sent out? I use the email settings for one of my sites (not using EC2) that sends out email after a user submits a form. What does it mean I shall call Amazon SES from an EC2 instance directly?