There are many crawlers, and I’m confident at least a couple have tried to connect to your server (unless you have an IP firewall, or if you’ve changed Plex Media Sever’s default port, in which case significantly less likely).
I assume it’s not really about them watching content, but to avoid them exploiting any possible PMS bugs.
Without direct connection, PMS uses Plex Relays, which limit streams to like 320p.