Reasons for not replying?

Writing on behalf of a friend who has been torturing herself over why a guy hasn't replied to her text.

He's her gym instructor, and she's been doing his classes for about a month; they've never really had a proper conversation apart from her asking him advice about some exercises, and he gave her a card with his website and mobile number on.

It was his last lesson and she didn't manage to get to ask him out in person, so she texted him saying that she had really enjoyed his classes and would miss him, and wondered if he'd be up for giving her more advice one day over a coffee.

That was 48 hours ago and he hasn't replied, which she is understandably upset about. She's been asking herself if it's the way she worded the text ,if he knows who she is etc. But in any case he knows she's one of his clients.

I even rang his mobile and hung up ( I know) just to see if the phone worked and if it was the right number, which it indeed was. She's looking for all kinds of solutions like maybe he's shy, he doesn't know what to say, the text wasn't clear, he's waiting to see her in person etc.

What does anyone else think? Feel bad for her as it's clearly hurt her. Myself I think it's really impolite of him to not even reply and I'm quite annoyed for her, but I think the likely thing is that he's with someone else or not interested, even if he could have had the decency to reply. Any other opinions? Thanks