The August 2013 ruling by the Texas Supreme Court to disregard cannon law regarding church property is what triggered the action to leave PCUSA. As others correctly stated - originally Dr Bell was of the conviction to stay in PCUSA and fight efforts to move the denomination in wrong directions. After 20 years, HP Pres was finding it a) difficult to attract conservative ministers b) our mission partners were becoming uncomfortable working with a church part of a denomination proposing crazy things, and c) the local Synod was increasingly dictatorial - 1) it seized control of 1st Presbyterian in Longview, dismissed the pastors and disbanded the church session, and 2) was going to censor the list of ministers the church could consider for hiring as its Sr minister.
If you want to get in the weeds, unlike a lot of churches, when HP Pres was originally founded in the 1926, the founders set up a trust to own the land and buildings, and a separate corporation to operate the church. The property trust had an agreement to let the operating group use the property - and that operating group was the one that was affiliated with a Presbyterian denomination. Amazing how prescient the founders were 86 years ago.