Those die-hard small phone users were probably aware of the mini. The first news about 5.42" came out in early 2019 from DigiTimes. Then Korean news reports called it in late 2019. Then Kuo.
If you look at the data, the SE2 attracted a lot of Android switchers and it wasn't a coincidence. The $399 price tag was very attractive. Most consumers don't cross shop between $399 and $699 devices.
Aware, certainly. Battery was already super bad on our iPhone SE1 and 7 though and OLED is iffy since I get migraines so I bought the SE2 asap. Just could afford to wait any longer. Prior to the SE2's release, I was prepared to buy the iPhone 8. Blessing in disguise, it was never in stock at Apple's refurb store and I didn't fancy paying MSRP nor tying myself to a 30-month contract just to get it discounted.
Even if the 12 mini and SE2 were both $399, I'd still get the SE2. With that said, the lower price would've made it easier to buy the 12 mini sooner for use as a "testing" device (for 5G and OLED/PWM).