In BrE, it's quite common to use "How many + noun?!" as an exclamation/question.
When Mike MC says 'exclamations', he's talking about a particular sentence form, not about exclamatory utterances in general, and not about interrogatives or reduced interrogatives (which is what I think you might mean here).
Grandma! What big teeth you have!
Oh, look! How lovely.
Thank you. How kind.
How sweet it is to be loved by you.
In these sentences, there's no questioning going on. In the final example, the part reading
How sweet does not in any way elicit a graded answer (i.e., very sweet, quite sweet, etc.) It's very different in meaning from that in, say,
How sweet do you like your tea? where there's a sense of degree of sweetness.
Similarly, when we use the words
how many, we're talking about degree in a similar way (number is essentially a kind of degree). So in sentences with embedded questions, such as
I don't know how many times I've told you not to say that or in short reduced exclamatory utterances like
How many more times?!, the idea of number is equally there. In the OP sentence, it isn't there.