It sounds like a guarantee from me that you will be fine. It is not quite that, and the gap catches people out, so let me close it.
What it is promising
That I teach it with options in it. I will offer a version of most things that a newer body can do, and I will not leave you stranded.
That is a real and meaningful promise about how the hour is run.
What it is not promising
That the room will be full of beginners. Usually it is not. An all levels class in a studio with a long-standing community is mostly people who have been practising for years, and the beginner in it is the exception.
That is fine, and it is also a completely different psychological experience from what the label implies, and nobody warns anybody about it.
The practical consequence
You will be offered the accessible version and you will be able to see eleven people doing the other one. Taking the option you were offered, in a room where almost nobody else is, requires a certain amount of nerve.
That nerve is the actual skill being asked for in your first month. Not strength, not flexibility. The willingness to do the smaller version while visibly surrounded by the larger one.
How to make it easier
Tell me before it starts. Ten seconds. It changes how much I watch you and it means the option arrives with your name on it rather than as a general offer to the room.
Put yourself where you can see the teacher rather than at the back, which sounds like the opposite of what a nervous person wants and is not. At the back you can only see other students, and other students are the wrong reference.
When to look for something else
If you have an injury, if you have never done any of it, or if the idea of the above makes you decide not to go, then a private class first, or a genuinely introductory class, is the better door.
Ask me which is which. You will get a straight answer, because the person answering the messages is the person teaching the class.