(I am not a lawyer but) in my opinion absolutely no - having it publicly accessible doesn't stop you from changing licenses on a per-file basis.

Even having a repo on GitHub doesn't mean it's actually usable - the absence of an explicit license means "All Rights Reserved" aka proprietary.

I can see your repo defaults to ISC license but just because that's true doesn't mean you can't do a per-file or post license. Several Open Source projects have subsets of different licenses in use across the codebase and as long as they're explicit and compatible it's all good.

Everything in my site defaults to AGPL-3.0 but then I've got post-specific overrides to make them Creative Commons / Apache-2.0 / otherwise as appropriate