I thought the problem with chocolate is theobromine, same effect as you describe, but bitter and comes from cocoa, so less sweet / more expensive chocolate with higher amount of cocoa is actually more dangerous.
But still, as with any poison, the dose is important, this veterinary page says “One ounce of milk chocolate per pound of body weight is a potentially lethal dose in dogs”, so a dog would need to eat 1/16th of its own weight for it to be deadly, even for small dogs that’s more than a whole bar.
This really isn’t a zsh problem, but a “people putting too much stuff in a ‘getting started’ config”.
I used zsh for 15 years before looking at any plug-in manager, you can get a lot of the good stuff like the completion by just going through the first-run wizard included in zsh. A lot of stuff is included directly with zsh, including various prompt themes (which is what that tutorial wants extra fonts for, because they use a fancy prompt with custom glyphs; I don’t think any of the built-in ones need that)
Things like fuzzy history search with fzf is usually included with fzf’s distro package and the additional zsh-completions package for less used or newer commands is also packaged by most distros. In my experience, a lot of the other plugins are stuff that could be a standalone script instead of a plug-in anyway.