They are not doing that. Matomo anonymous Ip is separate (and google and others use similar features).
They claim no cookie consent is needed because:
* tracking cookies are not used
* the data is not used for any other purpose than analytics
* a user cannot be tracked across days within the same website
https://matomo.org/faq/new-to-piwik/how-do-i-use-matomo-anal...
Reality is EU website sets a 13 month cookie, they clearly explain they will track a lot of data about you.
Anyways, some folks here claim that just using things for analytics is NOT an allowed exception to GDPR notice rules. I mention this to just again show that GDRP is not simple (despite claims here that it is "so easy").