The sentence would be okay if he had used a colon or perhaps a comma after "be," not a period.

I'm not an expert, but that's what I think.

I am sort of a grammar expert since I was a copy editor for 16 years.

writer of this is an internet grammar nazi.

Sometimes style trumps stodgy grammar.

Elmore Leonard was a master of this.

At first she could not see who it was.
Then the door swung open and in the streetlight she saw him.
Thomas Jackson.

Just my 2 cents.

I agree that a colon after "be" would be better punctuation than a period.

In the Leonard example, the lead in "It was..." is implied, and not stated to increase dramatic effect.

"Shut the door," is another example. In a command sentence, "You" or "You should" is often implied.

Grammar is a tool to be used, not a channel to be followed blindly.

Anything important deserves a proofreader, maybe an editor too. (Most written things are not important.)

I laugh at anyone who criticizes my grammar. If they want to fix it, fine, they can fix it. Cut, paste, edit, on their own computer. But please, don't bother telling me about it unless I've asked for your opinion.

Rarely I'll proofread and edit these posts on DU; usually I just let them fly.

If I was always thinking about where to place each foot I'd never be able to walk, much less run. If I thought about grammar then reading and writing would become a chore.

The language I write belongs to me. I own it. I tell the language what to do, it doesn't tell me.

"Sarah Will," for examples, am example dandy sentences what could also being name

"In linguistics, a register is a variety of a language used for a particular purpose or in a particular social setting".

So I think the above is okay as an example of colloquial or conversational English.

It's also an example of the concise style of writing found in "hardboiled" fiction.

But I agree with other posters that a colon or dash would be more appropriate. I would probably use an ellipsis...for greater effect!