Patent cases (as well as many others) are heard in the Federal Court system. The Federal Courts are organized into circuits [1]. In this case, Texas is in the Fifth Circuit.
Circuits are divided into Districts. Each District has a pool of District Court judges that hear cases. The Circuit has a whole has an Appellate Court (eg the Fifth Circuit Court of Appeals).
In large geographical Districts (as is the case in Texas and elsewhere), the Districts can be further divided into Divisions. The District itself organizes its District Court Judges into Divisions. The intent here is that you shouldn't have to drive 5 hours to get to the court that would hear your case.
So if you look at the Division Map of Texas, specifically for the Eastern District of Texas [2] you will see a lot of Divisions but the area is relatively low population so each Division might only have 1 or 2 District Court judges in it.
Federal District Court judges are nominated by the President and confirmed by the Senate but they're also, by convention, sponsored by a Senator in their home state. This is called the "blue slip" system [3].
So the Fifth Circuit ends up being quite conservative beccause the nominees tend to be those that a Senator from a very conservative state (nearly always a Republican) has to sponsor and generally only a Republican preisdent will nominate them. The opposite happens in the 9th Circuit, which includes California.
Cases are typically randomly assigned between all eligible judges. There are limits though like if a judge has already met their case load quota, they may be excluded from the assignment.
That means that if you find a judge who is friendly to your cause, you can establish a nominal business in the relevant Division and then file your case. This is called "judge shopping" and is precisely happens in the Eastern District of Texas for patent cases.
It's also why a lot of the more controversial political cases that go up to the Supreme Court in recent years have come from the Fifth Circuit: judge shopping in Texas.
Judges have an awful lot of power in civil and criminal cases and are almost entirely immune to lawsuits and prosecution for their use of discretion ("judicial immunity"). Judges get to decide scheduling, how much time to allocate to the trial, how many motions are allowed, how long those motions are allowed to me, how much evidence can be presented, scope of testimony, admissible evidence and so on. This can all add up to being a pattern of being very friendly to certain case types or plaintiffs.
And the plaintiff essentially gets to pick the venue where to fight the case.
[1]: https://www.uscourts.gov/sites/default/files/u.s._federal_co...
[2]: https://ballotpedia.org/File:Eastern_District_of_Texas.png