Encrypted connection, and therefore secure - what to do with it?

Question

HTML

The question in the title very accurately captures the essence of the problem I'm having.
The quest from the customer looks like this:

Draw a website with one page with a picture and an email send form.
Close the form itself with https (there is a certificate) to ensure security.

That is, literally - the inscription "if you are interested in our project - write your email, we will contact you." Everything. No other fields. An image, 5 words of text, an email input field and a "send" button.
Of course, I'm too smart, I asked why they need https?

https is an encrypted connection, so it's secure - mail.google example

I’m sitting here and thinking - am I an idiot and don’t understand something in life, or has the customer picked up clever words and doesn’t understand what he needs?
And most importantly, what to do with it?
PS Psto reflections, sorry if it's completely off topic ;-)