There is partial truth in what you have been told. A pecan tree tends to either produce nutlets before it sheds pollen or to shed pollen before its nutlets are receptive to the pollen. The two dollar words for these are protogynous and protandrous. When you have one of each type they can pollinate each other. Just planting two different varieties is not necessarily adequate, if they are both protogynous, for example. These distinctions are significant when you have a tree in an isolated area where there are no other trees to help pollinate it.
However, if you have other pecan trees (or even hickories, their close kin) in the neighborhood it will most likely not be necessary to plant two trees of different types. There will already be plenty of pollen drifting on the wind throughout the pollinating season. So either type will be covered.
For more information and a list of recommended pecan varieties for Texas (including which shed pollen early and which shed pollen late), check out the following web page:
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