I did ask her why she gave me her number and she said that she thought I was “cute” and wanted to talk to me.
We talked a little longer and then she stopped responding again…which irks me
The issue of whether she was available to be talking to “cute” guys didn’t come up.
Would it be weird to ask her point blank why she stops texting me and if she has a boyfriend?
As tough as this may sound, you may likely never get your answers. You must conquer your curiosity in order to avoid being wrecked by women. You must basically learn to live without the answers and I promise at that point things do become easier. You’re no longer held hostage of her storyline (meaning you are not compelled to wait for the subsequent pages of the story
she writes, you can live on your own without a conclusion (a conclusion from her, to be clear)).
People who stop responding like that have issues. Those issues may come down to work or tiredness or they may be the result of learning about a red flag or whatever. In my experience, “whatever” is the likeliest answer. This is where conquering your curiosity comes important. You need to get over wanting to know what exactly (or approximately) kind of “whatever” this is.
Asking point blank works sometimes and is a good strategy if you use it with reason but it has the potential to create mess. As Sun Tzu wrote, if you pin the enemy to the wall without leaving him a way of escape, there’s gonna be mess because he will be fighting for life.

Also, don’t ask point blank about suspicions. You’re likely to be wrong and even if she did some other wrong or strange thing, such an objectively false accusation could make her feel wronged, hurt, alienate her etc. Always suspend judgement until you have real proof; you have no idea what kind of “solid” cases blow up in the air when a new witness steps up or some new evidence is found. And in fact, sometimes people actually are completely innocent or just victims of circumstances. Better to stay your hand before you do something drastic, such as verifying your hypotheses with them. You can simply ask her to explain her behaviour but I’d do that face to face, not on the phone, as phone distorts voice, you don’t see face expressions etc., so more gaps are created than covered in such situations.
Sounds grim, I know, but lighten up. It’s not actually as bad as it sounds. You just had a girl give you her number and then vanish before anything remotely serious worked out. No real damage was done. You probably didn’t even take an ego blow, it’s just the curiosity. Deal with the curiosity and it’ll get better.

Also, if the girl is some poor confused creature, you might actually find you have sympathy for her. At any rate wish her well, life’s too short for holding grudges and God wants us to forgive and be generous about it (so that He could treat us the same way and each of us has a long account).