Most examples you'll see of `straight.el`/`use-package` configurations will have some version of: `(use-package something-cool :ensure t :config ...`. The `:ensure t` clause will cause it to fall back on `package-install` in the event it's not bolted into your local Cargo-style-own-the-world-and-dont-break repo mirror. Disks are big, it's like the right default now.
But if you've got a package that's mis-specified in terms of where on `github` or wherever that `striaght` is supposed to find it, you can find it tapping `elpa.org` on the shoulder at a time when the UI thread is also doing blocking network IO.
The `Messages` and/or `straight` buffers will have warnings about this, so it's fixable to find the offending package and it'll stay fixed, but in fairness what you're describing is possible.