What the ...? How did they find my personal email from my Github account?

it is easy. just append

.patch

to any commit hash url. unless you specify in the settings that you don’t want to make it public which will fallback to some cryptic email address

Shitty move by them though. That's not how you reach out to potential customers.

it is easy. just append .patch to any commit hash url.

this explains why I'm being reached out on my personal email when I've hidden it on my github profile.

I have received quite a few of these emails. I either delete them, or mark it as spam.