Texts are less important than email, and less urgent than a phone call. It’s ridiculous to think it’s rude not to reply, especially for kids who probably get 5-10 texts an hour.
If something’s important enough to you that you want a definite response eventually, send an email. If it requires immediate communication, call. Don’t apply false rules of politeness just to get a response out of your kid!
Yes, they asked for a reminder, not a conversation. Parents have to choose their battles. Demanding non-standard behaviour in order to do a required parenting thing like helping your child remember stuff is a really stupid hill to die on!