Texas has a relatively high poverty rate but low enrollment in medicaid. this suggests that:

This suggests that Texas has relatively stringent eligibility requirements for Medicaid.
A lot of people in Texas are very poor and they cannot afford to enroll in Medicaid. The rules to enroll in Medicaid are very stringent, which means that they are very strict, and that the requirements for eligibility are rather harsh, so not everyone can enroll in it - especially the poor.