Basically the sequence of events as claimed by the author is that:
XMPP small niche, small circles
Google launches Talk that was XMPP compatible
Millions joined Talk that could coop XMPP in theory
The coop worked only sparingly and was unidirectional, i.e. Talk to XMPP ✅ but XMPP to Talk ❌
Talk sucked up existing XMPP users as it was obviously a better option (bandwagon effect + unidirectional "compatibility" with XMPP)
Talk defederated
This demonstrated exactly the importance of reciprocity. If Meta plays dirty, defederate them then. Now is just too premature. Also frankly it is Meta that has more to lose than the fediverse at this moment as the bulk of users and thus the content are with Meta.