How do you explain it?

[AngleWyrm]

Glyn said:
The theory that “races will develop technology at a similar rate” implies that for any two races to be at the same tech level that would have had to have started at about the same time in the past. Another lose end that needs explaining.

Interstellar contact. The prime directive (Don't help anyone) is irrelevant, people will learn from each other anyway. Diplomats, Pirates, and other tradesmen will spread the technology around.