It's also not compressed at all - the english prose is 21 characters, over twice as long. Also the English prose requires at least ASCII, while the string of H can be encoded with a single bit each. 168 bits > 10 bits.

To be fair, it is faster to say, out loud, because our verbal "character set" is so much richer. A unit of pronunciation is roughly a syllable. "10 tosses, all heads" has only 5 syllables, while "ach ach ach..." takes 10. But this insight is a bit much to ask of someone new to the concept of compression.