I agree with you, but I wouldn’t read that much into their writing. The English language was even more lawless in their day.

In fact, the German-style capitalization of nouns may have just been a stylistic choice by the calligrapher:

Modern printings of the Constitution that follow the engrossed copy of the original can be identified by the many stylistic features in which Jacob Shallus’s calligraphy departs from the style of the printers of 1787. The most conspicuous difference is Shallus’s capitalization of almost all the nouns, in contrast to the very limited presence of capital letters in the work of the printers. The capital letters now help to give quotations from the Constitution, when taken from modern prints that follow the engrossed copy, an air of authenticity.

https://www.archives.gov/publications/prologue/2012/fall/const-errors.html