When the SE was released it had the same 2GB of RAM and A9 CPU as the 6s and 6s Plus, the latter of which was "the flagship". An iPhone with better internals wasn't released until 6 months later.
Maybe he means when the form factor was released originally as 5S.
The 4.87" x 2.31" x 0.30" envelope arose with the 5, a year before the 5S.
True, but there are some design differences (including the addition of TouchID), while the 5S and SE are almost identical. (You also mentioned the 5C, which was an alternative to the 5S.)
Sure. I mention the 5C because it was the real budget device. On the day it was released it had internals the same as the previous year's 5, instead of those of the 5S released on the same day as the 5C. The SE, by contrast, had the same guts as the 6s. People seem confused about this.