exec-path set correctly, but emacs does not find executable

Question

I am trying to export an org document to html, using the program bibtex2html, which I have installed:

$ which bibtex2html
/usr/bin/bibtex2html

Accordingly, I checked the exec-path variable in emacs:

("/app/bin" "/usr/bin" "/home/sean/.var/app/org.gnu.emacs/data/node/bin" "/home/sean/.var/app/org.gnu.emacs/data/cargo/bin" "/home/sean/.var/app/org.gnu.emacs/data/python/bin" "/app/libexec/emacs/27.2/x86_64-pc-linux-gnu/")

However, when I run the export command, which calls bibtex2html, I get the following message: Searching for program: no such file or directory, bibtex2html

I'm at a bit of a loss here. I tried using https://github.com/purcell/exec-path-from-shell, which I found from the answers at this question, but it did not help.

More specifics, as requested: I am trying to use org-export-dispatch to export the document to an HTML file. I am using doom emacs, and my keybindings for this command are SPC m e h h. Document export succeeds if I do not try to include a bibliography. I have (require 'ox-bibtex'), which in my doom/config.el file, as such:

(use-package! org-roam-bibtex
  :after org-roam
  :config
  (require 'org-ref)
  (require 'ox-bibtex))

I call ox-bibtex according to the documentation in its codec, by including the following line at the end of my org document:

#+BIBLIOGRAPHY: bibfilename stylename optional-options