That's true.
FYI, the reason is because that by taking Communion, the person would be saying through his actions that he believes what Catholics believe when taking Communion: that he is receiving the body, blood, soul and divinity of Christ. In effect, he would be lying through his actions. (But non-Catholics are welcome to attend Mass otherwise.)
OTOH, Christians in Orthodox Churches are permitted to take Communion in Catholic churches.
Permitted by us Catholics, not necessarily by their own Church's rules.
SD