San Patricio County must have voted GOP in absolutely HUGE numbers to outvote the southern portion of the district. CNN's election site confirms my theory, it looks like Farenthold got over 70% in San Patricio.
You can see data like that in my local township in suburban Crook County -- on election night, the Republican candidate for Congress out here (Wardingley, 1st district) and the Republican candidate for state Rep. (Bellar, 1 district) both WON suburban Crook County by decent margins. But they got crushed districtwide because the Chicago portion of those districts routinely gives RATs 90% of the vote and this election was no exception. Republicans would have to get 65%+ in my region of the district to outvote the improvised brain-dead RAT areas on the other end.
Cameron County on the border, while like 85% Hispanic, isn’t as heavily RAT as many people assume; in fact, President Bush carried it in 2004 and even when it votes Democrat it results in relatively few net votes for the Democrat because of it abysmal turnout (caused, no doubt, by having such a high percentage of non-citizens in its population).
The TX-27 has been marginal in presidential elections for years, and it finally trickled down to the congressional level. If someone like Farenthold could narrowly defeat Ortiz, imagine how well a Hispanic military veteran would have done in the district—Ortiz could have been blown out.