Because they're simply upending/ignoring Congressional mandates in the form of law. For example, Congress directed the creation of USAID as an independent agency in 1961. It cannot simply be abolished by executive fiat.
Sadly one of the references in that paragraph is a dead link now, because it references the USAID website which has been taken offline.
That doesn't seem to have happened, it looks like Rubio is now in charge of it. So again, how is this a coup?