I'm guessing you're right, but hoping you're wrong.
I don't keep herps (just field observe and photograph), but I decided to rescue this one (due to the likely hood of fatal injuries) for a few days of observation. IF he lives, I will offer him a meal tomorrow and watch him 2-3 days after feeding then release him at the point of capture. If he dies from internal injuries (my initial expectation) I will preserve and donate him.
As of now, he's sluggish and did not repeat the "blood spitting" when I just handled him briefly (first time since rescue). There is no apparent swelling, discoloration, or bleeding.
Two other possibilities: 1) maybe he bit his tongue or injured his mouth when biting me. 2) maybe he had just eaten some bloody road kill and started to regurge.
I'll post an update in a few days or if things change.
Note to TPWD lurkers: I've been advised that collecting DORs, rescuing and rehabbing injured herps, or moving at-risk herps from the roads is either not a violation of the new ban or will not be enforced as a matter of discretion. This snake will be rehabbed and released OR if he doesn't survive he will be preserved and donated to a museum.