It is a known problem that men can mistake friendliness for flirting.

For example:

When Men Mistake Friendliness for Flirting | by Tamara Mitrofanova | Fearless She Wrote | Sep, 2021 | Medium

There is a lot of discussion of this in the Google search:

guys mistake friendliness flirting

One idea is that embarrassment is likely to arise when a person faces a situation without a clear sense of the social expectations governing behavior...he or she does not know what to do next.

Embarrassment: A Form of Social Pain | American Scientist

I myself am confident that you handled things professionally/appropriately with that guy.