The text message is handled by airbnbs service and always comes on a local number. You'll notice when you start to get other queries from other guests it will also come through on the exact same number.
Your guests real number will be available to you once they book; you'll then be able to See their personal details on their booking form.
Part of the reason Airbnb does this is so you can't easily contact guests and make arrangements outside the Airbnb service.
There's actually no way to verify that the guest comes from where they say they do.
Lots of people open a profile but don't use it for a few years (me included). Ask questions and if your gut feeling is no, then say no. You are under no obligation to say yes. 50% of our guests are new to Airbnb and don't have a review. Good luck!
A great many of my guests are new without reviews, someone has to be first, right! You can always google them if you are uncertain, usually it verifies who they are pretty quickly.