While they were much more likely to capitalize nouns, and it did have German influence, it was never all nouns as in German, and it was absolutely used for emphasis during that period of time. If you read through letters by Franklin, or Thomas Jefferson, or many of the prolific writers of the Day, you'll see there are many nouns left uncapitalized, while seemingly important nouns (liberty, right, et cetera) are capitalized.

Here's a stack exchange comment thread that talks about it

I'd find you a better source but I'm on a road trip right now.

Capitalization in English is a super fascinating rabbit hole to fall down. Grammar in general, really. It was a lot more free form before the mid 1800s, and that allowed an author's voice to be a lot more personalized than in the modern day. Today, an author's voice is mainly due to their vocabulary choices, and to a lesser extent their punctuation, but during that time author's could choose different spellings, capitalizations, and other small idiosyncrasies that really let you get a feel for what their speech was like.