I think the author means well, and perhaps this is valid for a certain type of introvert, but these types of articles bother me. I'm an introvert and I have no problem with public speaking, I run my own company and I've been a manager over various teams and project, both large and small.
There is more than one definition of introvert - for me it's the one "A person predominantly concerned with their own thoughts and feelings rather than with external things." If anything, I'm self-centered and self-absorbed, but I am certainly not bashful. I've had it described to me as this: extroverts work out solutions by talking, introverts work out solutions thinking.
Meaning, I think internally, I mull over things in order to get them straight in my head, and I can work for days without speaking to a soul. But I am not shy, bashful or even remotely timid. I think people who use the 'I can't engage because I'm an introvert' would be better served by admitting they are shy and work on that. There is nothing wrong with having an introvert or extrovert mindset, and we need both in the world, but always equating introversion with bashfulness is a mistake in my eyes.