#1: As to truck size; in most states (pretty much all of them), a vehicle has to have a gross weight (combined or single) of greater than 26,000lb or a gross axle weight greater than 8,000lb (not 100% sure on the axle weight) to require a CDL.
#2: From the video I saw of the accident. It was a full-size conversion van, which are routinely used to transport up to 15 people(without requiring a CDL). Models such as: Chevy-GMC Express/Savanna, Dodge/Mercedes/Freightliner/International Sprinter/Ram Van, Ford Econoline and Transit are nowhere close to buses, but are regularly used.
As to texting while driving not being banned in Texas... Well, it's Texas.
I know that, that's why I'm glad Europe licenses are much more strict, some of that would be:
Commercial license is required for driving anything heavier that 7700lb and minimum age 21. And also for anything that carries more than 9 people.
Which means if you don't drive semi-truck rig or transit bus regularly, you are banned from driving most american pickups as well because they are heavier than 7700lb, this means that many guys like this are basically not allowed to buy them.
Getting a commercial license is very expensive and lengthy thing, and every 5 years health evaluation and re-testing is done which basically is turn off for everyone not being commercial driver, which is good.
Over here, driving is not a right you can have just because you are citizen or commodity you can buy and abuse, it's pretty easy to lose your license if you are caught driving recklessly, if you don't want to obey traffic code and rules of the road, you won't be driving, period.
Vans cannot be retrofitted to transporting people from cargo box, vans can transport people only if manufacturers make passenger version of them and seating is restricted to 9 people max(incl driver).
Texting or calling with phone in your hand is banned in entire region and fines are high if you get caught.
Laws like these, do save lives long term.