Is xenon electropositive in compounds of xenon?
How can a highly oxidized element be electropositive?


An element can be electropositive, the highly oxidized element less so. 

There are a number of things that don't sound quite right in the passage you quote.  For example, the Pauling electronegativity for xenon has been assigned (2.6, if you'd like to see the methodology used to caculate the electronegativity of a noble gas, see this earlier answer). Also, depending on the compound, hypervalent (or hypercoordinate) bonding, rather than use of d orbitals, might be used to explain the bonding in some noble gas compounds