Perhaps, but according to article:
"Astronomers are also finding out that the young stars in Orion have very little "elbow-room". Images obtained by Drs. Patience and MacIntosh as part of their on-going binary star survey in Orion suggest that "many stars in the sky are born under extremely crowded conditions," says Professor John Bally. "One of the Trapezium stars has no fewer than five companions, all within a few hundred AU." For comparison, the next nearest stellar neighbor to our Sun, alpha Centauri, is 4.35 light years (or over 270,000 AU) away."

Are all or most nurseries this crowded?

Was Sol formed in such a nursery?
How is that explained?

Unless near the galactic core I don't think stars this close are very common.

Or do these stars get ejected later?

If it's common for Stars to get ejected from the solar system, then it should as common for Planets to get ejected. Or if not planets what about Stars which didn't have time to form.
I also heard that gas giants are thought to form rather quickly- though perhaps such ideas are only due as response to this idea that gases evaporate quickly.

Also I'm not very impressed by such speeds as 20 km/sec- " and the gas and dust are evaporating away at roughly 20 km/s (43,000 mph)"- that's pretty slow in a solar system, and what exactly is "evaporating away" and how do we know it's not "merging together".