Interesting, maybe they block the orchestration servers of Tailscale, but not the actual data plane (which is almost always P2P, i.e., it usually does not involve Tailscale servers/IPs at all)?
I'm sure they do, but the question is, why did OpenVPN fail? It's pure P2P. I've got a dynamic DNS through afraid.org, and that resolves on that network, so it's not just DNS-level blocking. I effectively have a static IP anyway; there's no CGNAT going on, so I've discovered that I misconfigured my DDNS once or twice only when afraid.org emailed to tell me that I hadn't updated in X months.
Were you using the semi-well-known port (1194)? Otherwise, maybe it's just more fingerprint-able, or whatever DPI the firewall uses hasn't caught up to Wireguard yet?