In which county do you live. I think someone was pulling your leg. Texas has no party registration. If an election official actually said that, report that person the the Texas Secretary of State.
http://www.sos.state.tx.us/
You can vote in any primary you want. When you vote in a primary, your registration card will be stamped with the name of the party in whose primary you voted, and the county database will be updated indicate the party primary in which you participated. If you vote in the Republican primary you won't be allowed to participate in the Democrat runoffs and vice versa. If you are a candidate for office, you must only vote in your party's primary. Also, if you vote in any partisan primary, you can't give a valid signature for a third party candidate to get onto the general election ballot.
Didn’t Manfred say he voted absentee? He would have had to ask for either the democratic or republican ballot he wanted, right? I know he could have asked for either one, but perhaps that was his confusion?