we currently have a Referrer-Policy that doesn't share the referrer with third party sites, so your observation is correct.
it's a mechanism to reduce potential for user tracking.
this is similar to the default behavior seen on mastodon: https://github.com/mastodon/mastodon/pull/33214
i think the graph might not be fully accurate for the current hour? looking at it now it doesn't show that significant of a spike anymore. i don't see anything in our logs about federation issues from LW to p.d in the last 15 days.