Here's the exact text of the law:
SECTION 1. Article I, Texas Constitution, is amended by adding Section 32 to read as follows:
Sec. 32. (a) Marriage in this state shall consist only of the union of one man and one woman.
(b) This state or a political subdivision of this state may not create or recognize any legal status identical or similar to marriage.
There you have it. Because "any legal status identical... to marriage" sounds an awful lot like marriage to me....