Page cache not enabled for single product page.

I am using Hummingbird to do all the caching things.

And it works perfectly fine. But just for home page, when I see the source code, it shows some comments like this:

<!-- Hummingbird cache file was created in 2.1263468265533 seconds, on 11-01-18 7:25:35 -->

It help me confirming that the cache for this page was created. But if I move to sub pages like this one: https://www.**

And view the source code, it doesn't have the comment like the one home page had. This means the cache is not enabled in sub pages, right?