In a congregation where the Lord's Supper is thought to be a quaint remembrance of an event from long ago, open communion would likely be practiced. In a congregation where the Lord's Supper is a Sacrament, and the Lord is known to be truly present, probably not.
All took communion as seriously as Christ himself intended for it to be taken, and non would've batted an eye if a catholic present took the sacrament along with everyone else.
The Lord’s Supper is a sacrament in the Presbyterian Church. We believe that the Holy Spirit is present in the elements but do not believe in transubstantiation. Communion is open.
You are correct.