Sorry but I'm fairly confident it's spam - they just want you to look at their startup/substack links. That's why they included the links at all.

The compliment is a "foot in the door" so you don't immediately dismiss the email, and keep reading until the links.

I get the same type of comments on all my blog posts. Here's 2 examples directly from my blog:

"Awesome post! Keep up the great work! " (+ a link to their SEO service)

"Nice website, love the theme! Can I use it?" (+ a link to their WP service).